SAT Math Multiple Choice Question 904: Answer and Explanation
4. Using a riding lawnmower, Joe can cut his lawn in 45 minutes. Using a push mower,Joe's son can cut the lawn in 3 hours. If they work together, how long will it takethem to cut the lawn?
- A. 24 minutes
- B. 30 minutes
- C. 36 minutes
- D. 40 minutes
Correct Answer: C
Category: Passport to Advanced Math / Exponents
Strategic Advice: This is a work question, so use the formula W = rt. When two people are working together, start by finding their combined rate and go from there. Don't forget to convert Joe's time to hours to match the units given for his son's time.
Getting to the Answer: Manipulate the work formula to find each person's rate. If W = rt, then. Use 1 for W because there is 1 lawn to mow. Joe can mow the lawn in 45 minutes (or of an hour), so he can mow of the lawn in 1 hour. Joe's son can mow the lawn in 3 hours, so he can mow of the lawn in 1 hour. Working together, they can mow of the lawn in 1 hour. Substitute this rate back into the work formula to find the amount of time it will take them to mow the lawn together:
Working together, they can mow the lawn in of an hour, which is equal to minutes, making (C) correct.