There are 15 workers in groups in .Each can do 1 units per day. All the workers started a job of 220 units. After each day, a worker who can do 1unit per day joined the group. Find the taken to days

Options

A. 11
B. 12
C. 13
D. 10

Answer

A

Explanation

On the mth day, (15+m-1) workers would work.
On the firt day, 15 wokers would work.
On the second day. 16 workers would work and so on.
Let time taken to complete the job be N days
`Job=underset(m=1)overset(N)sum(15+m-1)=220`
`underset(m=1)overset(N)sum(14+m)=220`
`16+16+17+........+(14+N)=220`
Expression the RHS as a sum of consecutive natural numbers strting from 15, we have `15+16+17+18+19+20+21+22+23+24+25`.
`:.14+N=25`
`:.N=11`