A certain number of men can finish a task in 70 days. If 10 more men are added to the existing staff, then the task can be finished in 10 days less. How many men were there originally?

Correct option is C

Given:

A number of men can complete a work in 70days

If 10 more men are added then work is completed in 10days

Formula Used:

Work done = Number of workers \times Time

Let number of men, total days be M,D.

Then, $$M_{1}\times D_{1}= M_{2}\times D_{2}$$​​

Solution:

Let the number of men initially be x

Then total work will be = x \times 70

Now the number of men increased by 10 : (x+10)

Then time taken = 7 -10 = 60 days

​$$M_{1}\times D_{1}= M_{2}\times D_{2}$$​​

​$$x\times 70= (x+10)\times 60$$​​

70x = 60x+600

10x = 600

x = 60