Hands-on math!

Washington State Math Olympiad
Hints and Solutions
2014 Grade 5 Number Sense



Problem
Hint
1) Mrs. Roscoe noticed at the dance that for every three boys that walked in the door there were five girls with them. When she counted the tickets she found that the total number of boys and girls at the dance was 248. How many girls attended the dance?
Method 1: Use fractions:
1. Out of every ___ students 5 were girls.
2. The fraction that were girls is ____.
3. That fraction of the total is ____.
Method 2: guess-and-check. Just make sure your guesses for the number of boys is divisible by 3. Here is the table:
# boys#girlsTotal
120200320
   
   
   
   
   
2) William needed to change the oil in his truck. His truck holds 12 and 3/4 quarts of oil. Behind the seat he finds 2 and 3/5 quarts of oil. On the shelf in his garage he finds 3 and 2/3 quarts. How many additional quarts will he need to purchase? You need to add and subtract fractions with different denominators:
1. Add the amount of oil that William already has: = _____
2. Subtract that from the amount his truck holds = _____ quarts.
3. Since he must purchase whole quarts, round this up to the next whole quart = ______ quarts.

3) Tyree and Huang Fu are studying a set of new words for Spanish class. They both decide to make study cards. Tyree writes 7 words on each card except the last card has 6 words. Huang Fu writes 9 words on each card except the last card has 7 on it. What is the smallest number of words there could be in the whole set?
Fill in the following table: (M is the total number of words)
 N M =
7 x N + 6
Remainder of
M/9
1134
   
   
   
   
Keep incrementing N until the remainder of the division by 9 of M is 7.

Problem
Hint
4) Tammy is preparing to display all her rocks on a 28 inch by 22 inch poster board. Each rock will be in its own square with side length 3 and 1/4 inches, which fits her largest rock. The maximum number of squares that fit on the poster board is the same as the number of rocks in her collection. How big is her collection? 1. Divide 28 by 3.25 = _____ and round down = _____.

2. Divide 22 by 3.25 = _____ and round down = _____

3. Multiply these two numbers together to get the number of rocks in Tammy's collection = _____.

5) Roni loves to talk. Roni's mom is a tech wiz and programs Roni's phone so that after 7pm, each time she is on her phone it cuts her off at half of the time she spent on her previous conversation. Her first phone call lasts 52 minutes and starts at 7:05 pm. If she talks until she is cut off in every conversation after that, how many minutes has she been on the phone at the end of her sixth call? Express your answer as a mixed number.
Fill in this table:
Call #Length (min)
152
2 
3 
4 
5 
6 
Total 
Sum the call lengths of the 6 calls. = _____ minutes.