Click here for the Problem Extension Worksheet version of the Problems of the Week.
Click here for an MS Word version of the Problems of the Week.
Click here for the Canadian Problem Extension Worksheet version of the Problems of the Week.
Click here for a Canadian MS Word version of the Problems of the Week.

Lower Elementary:
Question: Willy bought a candy bar for 99¢ and a bottle of water for $1.26. If he pays with a $5 bill, what is Willy’s change?
Answer: $2.75
Solution: The total amount Willy spent is 99¢ + $1.26 = $2.25. Because he pays $5, he will receive $5.00 – $2.25 = $2.75 as change.

Upper Elementary:
Question: Tiffany arrived at the airport at 3:50 PM. Her flight was supposed to leave at 5:15 PM, but it was delayed for 2 hours. How long was Tiffany at the airport before her flight left?
Answer: 3 hours and 25 minutes
Solution: The plane left 2 hours after 5:15 PM, which means it left at 7:15 PM. It is 25 minutes from 3:50 PM to 4:15 PM and then it is 3 hours from 4:15 PM to 7:15 PM, so the total time Tiffany was at the airport was 3 hours and 25 minutes.

Middle School:
Question: There are three candidates for class president. Becky received 25% of the total votes. Charles received 45% of the votes. Daniella received 300 votes. What is the total number of votes in the election?
Answer: 1,000 votes
Solution: We need to find the percent of the votes that Daniella received. From 100% of the votes, Becky has 25% of the votes and Charles has 45% of the votes. So Daniella has 100% – 25% – 45% = 30% of the votes. Since 300 votes represent 30% of the total votes, that means that 100 votes represent 10% of the total votes. So 1,000 votes represent 100% of the total votes.

Algebra and Up:
Question: Gerald can paint a fence in 2 hours. Mandy can paint a fence in 3 hours. How long will it take them to paint a fence together?
Answer: 1 hour and 12 minutes
Solution: Gerald can paint 1 fence in 2 hours, so his rate is 1/2. Mandy can paint 1 fence in 3 hours, so her rate is 1/3. If we let x be the rate at which they can paint a fence together, they can paint 1 fence in x hours, so the rate is 1/x. So our equation is:
1/2 + 1/3 = 1/x
Combine the fractions.
5/6 = 1/x
Find the cross product.
5x = 6
Divide by 5.
x = 6/5 = 1 1/5
Together, Gerald and Mandy can paint a fence in 1 and 1/5 hours, or 1 hour and 12 minutes.