Question

A is twice as good as a workman as B. And together, they finish a piece of work in 20 days. In how many days, will A alone finish the work?

• A. 30 days
• B. 25 days
• C. 26 days
• D. 28 days

Answer 1

Answer:

A. 30 days

Solution:

Given:

A = 2B

Concept used:

if A can do work in n days then one-day Work will be 1/n 

Calculation:

A is twice as good as B '

∴ time taken by A be x days and time taken by B be 2x days 

1/x + 1/2x = 1/20

$\frac{2x+x}{2x^2}=\frac{1}{20}$

$\frac{3}{2x}=\frac{1}{20}$

$2x=60$

$x=30$

A alone finished work in 30 days

Shortcut Trick

 A is twice efficient as B 

∴ A = 2B 

⇒ A/B = 2/1

⇒ A + B = 3 

Total work = 20 × 3 = 60 

∴ A alone can finish work in = 60/2 = 30 days