Fifteen painters can paint a number of houses in 12 days .if the number of painters is increased by 5, how many days less would it take the painters working at the same rate to paint the houses?

Answer 1

clearly a painter can paint 1/180 of the job in one day. So, 20 painters can paint

20/180 = 1/9 of the job in a day, making the total 9 days.

So, it takes 3 days less.

Not also that you could reason that if the number of painters is increased by a factor of 5/4, the time taken is reduced by that factor.

4/5 of 12 = 9