Hands-on math!

Washington State Math Olympiad
Hints and Solutions
2016 Grade 5 Number Sense

Problem
Solution
1) Jason is playing with a stack of cards. He divides the cards into 3 equal piles. Then he takes one pile and divides it into 4 equal piles. Then he takes one of the four equally divided piles and further divides it into 5 equal piles. If one of the five equally divided piles contains 3 cards, how many cards in total are in Jason's stack? Work this problem backwards:
1. If Jason has 5 piles at the end and each pile contains 3 cards then those 5 piles contain 15 cards total.
2. If those 5 piles were 1/4 of the cards in the previous step,then the 4 piles together contain 60 cards.
3. Those 4 piles are 1/3 of the deck, so the whole deck contained 180 cards.
2) The sum of two numbers is 22 and their product is 96. What is the ratio of the two numbers when expressed as a proper fraction in lowest terms? 1. Write out the 2 number factors of 96:
    32 x 3   16 x 6   8 x 12   4 x 24   2 x 48
2. Find the two that sum to 22 = 16 and 6.
3. Express the ratio of these two numbers =
    6/16 = 3/8
3) What is the greatest common prime factor of 78 and 117? 1. Write out the prime factors of both numbers.
    factors of 78   = 39 x 2 = 13 x 3 x 2
    factors of 117 = 39 x 3 = 13 x 3 x 3
2. The largest one in both lists = 13
4) A costume store has a sale. All costumes are being sold at a discount and are 25% off the original price. One costume has a tag that marks it for an additional 10% off the discounted price. If the original price of the costume is $50, what is the final sale price (not including tax)? 1. The discount price is $50 - 25% of 50 =
    $50 - $12.50 = $37.50
2. A further discount of 10% off this price is $3.75.
3. Subtract this from the first discount price to get the final sale price = $37.50 - $3.75 = $33.75

5) A group of children are picking apples in an orchard. Kyle collects 28 apples, Rachel collects 33 apples, Lima collects 39 apples in a day. They want to make $200 for a trip they are planning. If they get $2 for every 25 apples picked, how many days will they need to pick apples to make enough money for their trip?
1. What is the total number of apples picked in a day by all kids? = 28 + 33 + 39 = 100 apples
2. Divide this by 25 = 100 apples/25 = 4.
3. Multiply by $2 to get the amount the kids get paid per day = 4 x $2 = $8 per day.
4. Divide the cost of the trip by this amount to get the number of days = $200/$8 = 25 days