Question

How many days?

Answer 1

20

Explanation:

Updated:
So the job takes 360 man-days to complete.
360/15=24 days
18 men would need to complete it in 360/18 or 20 days.

Or

`15*24 = 18*days`

`360 = 18 days`

`20 = days`

Answer 2

We can clearly see that this is an inverse proportion question, in that case, the rule is,
`x_1xxy_1=x_2xxy_2`
Here, let `x_1` be electricians, in the first case the number of electricians are 15, and the date(`y_1`) is 24
Here, `x_2` is 18, and `y_2` is unknown. So,
`15xx24=18xxy_2`
Divide both sides by 24
`(15 xx cancel24)/(cancel24) = (cancel18^3 xx y_2)/(cancel24^4)`
We get
`15=(3xxy_2)/4`
Multiply both sides by 4
`15xx4=(3xxy_2)/(cancel4)xxcancel4`
We get
`60=3xxy_2`
Divide both sides by 3
`(cancel60^20)/(cancel3^1)=y_2`
We get
`20=y_2`
`therefore 18` electricians would require 20 days