Question

A can do a piece of work in 7 days of 9 hr each and B can do it in 6 days of 7 hr each How long will they take to do it working together $\frac{42}{5}$ hr a day?

• A. 3 days
• B. 4 days
• C. 4.5 days
• D. None of these

Answer 1

Answer: (A)

3 days

A can complete the work in $7\times 9=63hours$
B can complete the work in $6\times 7=42hours$
A's one hour work$=\frac{1}{63}$
B's one hour work$=\frac{1}{42}$
(A+B)'s one hour work$=\frac{1}{63}+\frac{1}{42}=\frac{5}{126}$
$\therefore$Both can finish the work in$\frac{126}{5}hours$
Number of days of $\frac{42}{5}$ hours each=$\frac{126\times 5}{42\times 5}=3days$