If 9 can assemble 10 in (20*7.5=) 150 hours, 1 can assemble 10 in (150*9=) 1350 hours.

In the new case, 2 people can work as much as 3 before. So 12 new workers = 18 old workers.

18 old workers could assemble 10 in 75 hrs and 20 in 150 hrs.

Working 6 hours a day, it would take the new workers 150/6 = 25 days.

True!!

Just wanted to share a formulae:

Workers(p) -Wp ; Workers(n) -Wn
Time(p) -Tp ; Time(n) -Tn
Job(p) -Jp ; Job(n) -Jn

***Make sure that the TIME is in one simple unit (hours/days)

Therefore Wp*Tp/Jp=Wn*Tn/Jn

total hours to assemble 10 units in 20 days with 7.5 hours by 9 workers=150hrs
Also 2 people can work as much as 3 before each. Hence 12 new workers = 18 old workers

9*150/10=18*Tn/20;

Tn=9*150*20/(18*10)

Tn=150 hours.

If working 6 hours a day 150 hours can be covered in = 150/6=25 days.

Hope this helps !

Layo wrote:In a TV factory 9 persons can assemble 10 tv sets in 20 days of 7 1/2 working hours. How long will it take for 12 persons to assemble 20 tv sets working 6h per day, it being given that 2 persons in the latter case do work as much as 3 men in the former?

A. 10
B. 12.5
C. 20
D. 25
E. 50

OA D

Please explain how to solve this.

Let rate per worker = 2 units per hour.
Rate for 9 workers = 9*2 = 18 units per hour.
Over 15/2 hours, number of units produced = r*t = 18*(15/2) = 135 units.
Over 20 days, number of units produced = 20*135 = 2700 units.

Since 20 TV sets are twice the work, new work = 2*2700 = 5400 units.
Rate for 2 faster workers = rate for 3 regular workers = 3*2 = 6 units per hour.
Thus, rate for 12 faster workers = 6*6 = 36 units per hour.
Over 6 hours, number of units produced = 6*36 = 216 units.
Number of days needed = w/r = 5400/216 = 25.

The correct answer is D.