Solve the problem.
-Martha can rake the leaves in her yard in 2 hours. Her younger brother can do the job in 7 hours. How long will it take them to do the job if they work together?
A) $\frac{9}{14} \mathrm{hr}$
B) $\frac{14}{5} \mathrm{hr}$
C) $\frac{14}{9} \mathrm{hr}$
D) $7 \mathrm{hr}$

Question

Quizplus · Accepted Answer

When working together, their combined rate is the sum of their individual rates. Martha's rate is 1/2 of the yard per hour, and her brother's rate is 1/7 of the yard per hour. Together, they can complete 1/2 + 1/7 = 7/14 + 2/14 = 9/14 of the yard per hour. Therefore, it will take them 14/9 hours to complete the job together.

Solve the Problem 914hr\frac{9}{14} \mathrm{hr}149​hr B) 145hr\frac{14}{5} \mathrm{hr}514​hr C) 149hr\frac{14}{9} \mathrm{hr}914​hr D) 7hr7 \mathrm{hr}7hr

Solve the Problem $\frac{9}{14} \mathrm{hr}$ B) $\frac{14}{5} \mathrm{hr}$ C) $\frac{14}{9} \mathrm{hr}$ D) $7 \mathrm{hr}$