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RD Sharma Solutions Class 8 Mathematics Solutions for Time and Work Exercise 11.1 in Chapter 11 - Time and Work

Question 15 Time and Work Exercise 11.1

A and B can do a piece of work in 6 days and 4 days respectively. A started thework, worked at it for 2 days and then was joined by B. Find the total time taken tocomplete the work.

Answer:

If A and B finish the assignment in x days,

A and B's one-day work is equal to 1/x.

The given details are,

A can do a piece of work in = 6 days

A’s 1 day work = 1/6

B can do a piece of work in = 4 days

In 2 days the work completed by A = 2 × 1/6 = 1/3

part of work Remaining work = 1 – 1/3

= (3-1)/3

= 2/3

A and B can finish the remaining work in = (2/3)/(1/6 + 1/4)

= (2/3)/(5/12)

= (2×12)/(3×5)

= 8/5 days

∴ Total time taken to complete the work by A and B = 2 + 8/5

= (10+8)/5 = 18/5

= 3 3/5 days

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