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

Solution;

E and F can together complete the work in 10 days.

Efficiency of E+F = $\frac{1}{10}$

E alone can do it in 30 days.

Efficiency of E = $\frac{1}{30}$

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

$=\frac{3-1}{30}$

$=\frac{2}{30}$

$=\frac{1}{15}$

F alone can complete the work in 15 days.

Alternate Method:

Suppose, Total work = 30 units (LCM of 10, 30)

⇒ Efficiency of F = 3 – 1 = 2 units/day

∴ F alone can complete the whole work in = $\frac{30}{2}$ = 15 days