A group of 40 mechanics working together have to complete a piece of

Question

A group of 40 mechanics working together have to complete a piece of work in 30 days . If all the mechanics work at constant rate and after 20 days , it was found that only 1/4th of the was completed ,then how many more mechanics should be recruited so that work gets completed on time ?

A. 32
B. 100
C. 200
D. 240
E. 280

I calculated total work = 40 x 30 = 1200, why can't we use this as total work.

A. 32
B. 100
C. 200
D. 240
E. 280

gmatophobia · Answer

Let's assume that each mechanic can do 1 unit of work per day.

40 mechanics over a period of 20 days will complete, 40 * 20 units of work i.e. 800 units of work.

This 800 units represents 1/4th of the work, so total work is 4 times 800 i.e. 3200 units.

Work Remaining = 3200 - 800 = 2400

Number of days remaining = 10

Work required to be completed per day = 2400 / 10 = 240

We already have 40 men, therefore we need 200 more men to complete 240 units of work per day.

Option C

chetan2u · Answer

Since 1/4 work is completed in 20 days, the entire work can be done in 20*4 or 80 days. So, they require another 60 days work to finish the work.

The 40 mechanics have already worked for 20 days, so they are left with 30-20 or 10 days.

If 60 days are required by 40 mechanics, 60/6 or 10 days will be required by 40*6 or 240.

We are looking for ‘how many more’, so 240-40 or 200

C

Apeksha2101 · Answer

I calculated total work = 40 x 30 = 1200, why can't we use this as total work.

Bunuel · Answer

Because we are not told that 40 mechanics  can  complete the piece of work in 30 days. Instead, this is the  goal . Therefore, we cannot assume the total work equals 40 * 30 units.

The question is actually straightforward:

1/4 of the work took 40 mechanics 20 days. So, the remaining 3/4 of the work would take them 3 times as long, or 60 days. However, we want the work completed in just 10 days, which is 6 times faster. This means the workforce needs to increase 6 times, from 40 to 240 mechanics. Therefore, we need to add 200 more mechanics.

Answer: C.

A group of 40 mechanics working together have to complete a piece of

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