Some carpenters promised to do a job in 9 days but 5 of them were absent and remaining men did the job in 12 days. The original number of carpenters was:

20

Let there were originally x number of carpenter .

Total work = efficiency × number of days

Total work  = 9 × x = 9x

5 went on leave . So leftover carpenter does the work in 12 days 

total work by them = 12(x - 5)

As per questions,

9x = 12(x - 5)

9x = 12x - 60

 9x - 12x = 60

-3x = -60

 x = 20  is number of carpenters