Question

E and F can do a work in 10 days. If E alone can do it in 30 days, F alone can do it in ____ days.

• A. 15
• B. 20
• C. 25
• D. 18

Answer 1

Answer:

A. 15

Given:

E alone can doi it in 30 days

In one day E alone can do it in $\frac{1}{30}$ work

Calculation:

$\frac{1}{E}+\frac{1}{F}=\frac{1}{E+F}$

$\frac{1}{F}=\frac{1}{10}-\frac{1}{30}$

$\frac{1}{F}=\frac{2}{30}$

F alone can do it in $\frac{30}{2}=15days$.

Alternate Method:

E+F= 10 days

E =30 days

Efficiency of F = 3-1 = 2

F alone can do it in $\frac{30}{2}= 15 days.$