Meet #4. Park Forest Math Team. Self-study Packet. Problem Categories for this Meet (in addition to topics of earlier meets):

Transcription

1 Park Forest Math Team Meet #4 Self-study Packet Problem Categories for this Meet (in addition to topics of earlier meets): 1. Mystery: Problem solving 2. Geometry: Properties of Circles 3. Number Theory: Modular, Series and Sequences 4. : Percent Applications 5. Algebra: Word Problems (linear, including direct proportions or systems)

2 Important Information you need to know about ARITHMETIC: Percent Applications Change a percent to a decimal by moving the decimal two places to the left. Change a decimal to a percent by moving the decimal two places to the right and adding the percent sign. Of means multiply Is means equals Example: Find! % of 2000.! =.5!% = = 10 To calculate how much money you will have if you deposit x dollars at an interest rate of y% after t years, first change the interest rate to a decimal, then multiply the original deposit by the sum of one plus the interest rate raised to the power of t. Example: How much money will you have after 8 years if you deposit $10,000 at an interest rate of 6% a year? $10, !$15, *Be careful! Annual interest rate is per year. Monthly interest rate is per month. If you are told that the annual interest is 6% but that interest is compounded monthly, you need to find the monthly interest rate by dividing by twelve before you can compute.

3 Category 4 Meet #4 - February, 2015 Calculator meet 1) The "Rule of 72" is often used to approximate the number of years, Y, it would take to double the value of an investment when given an annual rate of R percent, as follows: (R)(Y) = 72. For example, if $50 were invested at an annual rate 6%, then it would take 72 / 6, or 12 years, for it to double in value to $100. If that same $50 had been invested at 4% instead, then how many more years would it have taken for the $50 to double in value? 2) Gronk took his 74 teammates out for a steak dinner. The average price for each dinner was $ A 5% tax was then added onto the cost of the meal. He left the wait staff a generous 35% tip, based on the price of the meal only. What was the total amount, including meal, tax, and tip, that Gronk paid so that he and his teammates could have dinner? 3) Early in the race, Jen and Berry were running at the same speed. Berry then increased her speed by 20% while Jen increased her speed by only half as much. Berry is now running at 60 spans per second. How many spans per second is Jen running now? Steve Jobs, born in February of 1955, was an American entrepreneur, marketer, and inventor who was the co-founder, chairman, and CEO of Apple Inc. He is widely recognized as a pioneer of the personal computer revolution, transforming one industry after another, from computers and smart phones (iphone) to music (itunes) and movies (Pixar). ANSWERS 1) 2) 3)

4 Solutions to Category 4 Meet #4 - February, ) 6 2) ) 55 1) Using the rule of 72, 72 / 4 = 18 years, which is 6 years more than 12. 2) (75)($76.80) = $5760, the total cost of the food only. ($5760)(0.05) = $288, the amount of tax. ($5760)(0.35) = $2016, the amount of the tip. Meal + tax + tip = $ $288 + $2016 = $ ) Working backwards, Berry's speed early in the race was 60 / 1.2 = 50 spans per second. Jen's speed now: (50)(1.1) = 55 spans per second.

5 Category 4 Meet #4, February 2013 You may use a calculator. 1. This year, an all-day adult lift ticket at Ski Mountain costs $78, which is 4% more than last year. How much did an all-day adult lift ticket cost last year? 2. The original price of a winter coat was $60 before it was marked down by 30% for a sale. Mary bought the coat during the sale but she also used a 10% off coupon. How much did she pay for the coat? Express your answer in dollars to the nearest hundredth of a dollar. 3. Allan deposited $10,000 into a savings account that paid 3% annual interest compounded monthly. Izak deposited $10,000 into a savings account that paid 4% annual interest compounded monthly. Neither of them withdrew any money from his account. After one year, how much more money did Izak have in his account than Allan had in his account? Remember that, each month, interest will be paid on the balance at 1/12 of the annual rate. Express your answer in dollars to the nearest hundredth of a dollar. 1. $ 2. $ 3. $

6 Solutions to Category 4 Meet #4, February The price of $78 represents 104% of the previous year s price. To find the previous year s price, we simply divide 78 by 1.04, which is $ $75 or $ $ $ When a price is marked down by 30%, it means the new price is = 70% of the old price, so the sale price of the coat was = $42. Mary also used a 10% off coupon, so she paid = 90% of the sale price, which was = $ We can calculate the year-end balances directly as follows: and After one year, Allan has 10, , = $ more than Izak. Alternatively, we could keep track of the balances at the end of each month, as shown in the table below. Allan's Izak's Month Balance Balance 0 $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10, $10,407.42

7 Meet #4 February 2011 Category 4 1. The tab for your dinner party at a restaurant came to. You want to leave a tip, and also need to add tax on the price of dinner. How much does the dinner cost altogether? (There is no tax on the tip, and assume you do not pay a tip on the tax either.) 2. If the price of a gallon of milk increases by, and the price of a gallon of oil decreases by, then both prices will be the same. What percent of the price of (a gallon of) oil is the price of (a gallon of) milk? 3. Your company, IMLEM Lemonade Inc., has purchased worth of supplies (lemons, sugar, paper cups). This is enough to make cups of lemonade. You sold of that number, for per cup. From the money you have left (the amount you received from customers minus the cost of your supplies), you pay in salaries. From the amount left, you pay sidewalk-tax to your parents. How much money do you have left? 1. $ 2. % 3. $

8 Meet #4 February 2011 Solutions to Category 4-1. The tax amount is The tip amount is Overall: Editor s note: The original problem did not say there was no tip on the tax. This would give $204, which was not allowed as an answer If we name the respective prices, then we know that: or: and so: 3. Our revenue (the amount we got from customers) is: Minus the cost of supplies, you have left. After paying salaries, you have left After paying tax, you have left

9 Category 4 Meet #4, February The Euclidean Middle School math team had a score of 120 at the 1 st IMLEM meet of the year and a score of 165 at the 2 nd meet of the year. What was the percent increase in the math team s score from the 1 st meet to the 2 nd meet? Express your answer as a mixed number. 2. Akeelah bought a dictionary that was on sale for 27% off. The sale price was $ What was the original price of the dictionary in dollars? 3. Frank went to the bank to deposit $6,000 in a new savings account. The bank had two offers for him. He could either earn 6% annual interest compounded monthly, or 7% annual interest compounded annually. At the end of 3 years, how much more interest will he have earned if he chooses the better offer than if he had chosen the worse offer? Assume no withdrawals or additional deposits were made during these three years. Round your answer to the nearest whole dollar

10 Solutions to Category 4 Meet #4, February The team's score increased by 45 points which is compared to the original score of 120 to find the percent increase. increase 2. $48 3. $ If Akeelah received 27% off, that means she still had to pay for 73% of the original price. Since she paid $35.04 we can use the following equation to find the original price, : 3. If Frank chooses to compound the interest monthly he would use this equation to find the value after 3 years: If Frank decides to compound the interest annually he would use this equation to find the value after 3 years: Using the second option he would have earned more.

11 Category 4 Meet #4, February 2007 You may use a calculator today! 1. If you increase Meghan s favorite fraction by 25% you get Eva s favorite fraction. The difference between their favorite fractions is 1. What is Meghan s favorite fraction if she always expresses it in lowest terms? The dinner bill for the party of nine people came to $240.65, before the sales tax was added. Jim calculated the amount of a 15% tip on the amount before the 5% sales tax was added. Craig calculated the amount of a 15% tip on the amount after the 5% sales tax was added. How much more would the waiter get if the party agreed to pay Craig s tip instead of Jim s tip? Express your answer in dollars to the nearest hundredth of a dollar. 3. A bank plans to offer a savings account at 4.8% simple annual interest. If the bank compounds monthly, what is the annual yield for this savings account? (The annual yield is the amount of interest a given balance would earn when the effect of the compounding interest is included.) Do not round until the last step, and give your answer as a percent to the nearest tenth of a percent

12 Solutions to Category 4 Meet #4, February $ Let s call Meghan s favorite fraction x. Then Eva s favorite fraction is x plus 25% of x. This can be written as 1.25x or 5 4 x. The positive difference between x and 5 4 x is 5 4 x x = 1 x. If x = 1 12, then 4 4 x = Meghan s favorite fraction must be 1 3, since she always expresses it in lowest terms. 2. The tip as calculated by Jim would be $ = $ or about $ The dinner bill after tax comes to = $ or about $ The tip as calculated by Craig would be $ = $ The difference between these two amounts is $37.90 $36.10 = $1.80. In general, Craig s method of calculating the 15% tip on the after tax total amounts to a slightly more generous tip of = = 15.75%. 3. With an annual interest rate of 4.8%, the monthly interest rate would be 4.8% 12 = 0.4%. As a decimal, 0.4% is 0.004, or 4 thousandths. Since the interest on the balance is added to the balance each month, the easiest way to calculate it is to simply multiply by If we multiply the original amount by each month for 12 months, the compounded value will be , which is about times as much. The annual yield is the extra 0.049, or 4.9%.

13 Category 4 Meet #4, February 2005 You may use a calculator 1. What is 135% of 4? Express your answer as a common fraction in simplest 9 form. 2. The store Mathletes R Us sells sweatshirts with different proofs of the Pythagorean Theorem. The manager purchases the sweatshirts from a distributor at a cost of $12.57 each. She marks up the price so that the price on the tag of each sweatshirt is 60% cost and 40% profit. At the cash register, the customer then has to pay a 5% sales tax on the tag price of the sweatshirt. How much does a customer end up paying for a sweatshirt with a proof of the Pythagorean Theorem? Give your answer in dollars to the nearest hundredth of a dollar. 3. Ron s grandmother sent him a check for $5000 and told him to deposit it in a money market account that earns interest at an annual rate of 3% and compounds monthly. Ron allowed 4 months to go by before he deposited the check. How much interest income did Ron lose by not depositing the check immediately? Express your result to the nearest hundredth of a dollar. Note: This particular money market keeps track of the nearest millionth of a dollar for purposes of calculating interest owed

14 Solutions to Category 4 Average team got points, or 1.2 questions correct Meet #4, February 2005 Average number of correct answers: 1.16 out of $ $ This problem is easier if we convert 135% into the equivalent fraction 27. Now we multiply as follows: = To mark up the sweatshirt so that the tag price is 60% cost and 40% profit, the manager asks herself the following question: $12.57 is 60% of what number? This corresponds to the equation: = 0.6x. The manager has learned to divide by 0.6 to answer the question. This gives a price of $ = $20.95 for the tag price of the shirt. The customer then has to pay a 5% sales tax on this tag price. We can compute the 5% by multiplying $20.95 by 0.05, which is $ or about $1.05. We then add this tax to the tag price for a total of $ $1.05 = $ Alternatively, we can find 105% of $20.95 directly by multiplying by We get $ = $ , which rounds to nearest cent as $ If the annual interest rate of the money market account is 3%, then the monthly interest rate must be 3% 12 = 0.25%. After interest is posted at the end of the first month, Ron s balance would be $ = $ Then he begins to earn interest on the interest as well as the original money from his grandmother. After the second month, his balance would be $ = $ After the third month, the balance would be $ Finally, after four months, Ron s balance would be $ , which rounds to $50.19 to the nearest hundredth of a dollar.