A group of men decided to do a job in 13 days but 9 men left the work after each day. The work, as a result, got completed in 16 days. How many men were initially in the group?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 360.
Let the total number of men initially be x.
According to the given question,
Number of men for 16 days = x, (x - 9), (x - 18),.....(x - 135)
Now, sum of n terms = (n/2)[(a + l)/2]
where a is first term, l is last term and n is number of terms in the series.
⇒ x + (x - 9) + (x - 18)....+ (x - 135) = 13x
⇒ (16/2)[x + x - 135 = 13x
⇒ 16x - 1080 = 13x
⇒ 3x = 1080
⇒ x = 360