How many days?

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2 Answers
Dec 1, 2017

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#

Dec 2, 2017

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