​A can finish a task in 20 days and B can finish the same task in half the time taken by A. Working together, what part of the task can they finish in a day? ​

Correct option is C

Given:

Time taken by A to finish the task: 20 days

Time taken by B to finish the task: $$\frac{20 days }{ 2 }$$​= 10 days

Formula Used:

Work done by A in one day =$$\frac{ 1 }{\text{ Time taken by A to finish the task}}$$​​

Work done by B in one day = $$\frac{ 1 }{\text{ Time taken by B to finish the task}}$$​​

Work done by A and B together in one day = Work done by A in one day +  Work done by B in one day

Solution:

Work done by A in one day = $$\frac {1}{20}$$​​

Work done by B in one day = $$\frac {1}{10}$$​​

Calculate work done by A and B together in one day:

Work done by A and B together in one day = $$\frac {1}{20}$$+  $$\frac {1}{10}$$​

Work done by A and B together in one day = $$\frac{1+2}{20}$$​​

Work done by A and B together in one day = $$\frac{3}{20}$$​​

Therefore, working together, A and B can finish $$\frac{3}{20}$$​ of the task in a day.

Alternate Method:

​​Work done by A and B together in one day =$$\frac{1+2}{20}$$ =$$\frac{3}{20}$$

Option (c) is right answer.