maths
posted by simranpreet on .
300 men were engaged to complete a job in a certain number of days. but due to another assignment fifteen men dropped the second day, fifteen more men dropped the third days and so on .if takes fifteen more days to finish the work now.find the number of days in which the work was completed. please hellllllppppp.

The number of manhours that were used were
300 + 285 + 270 + 255 + ... + 15 + 0
Since we can't count the + 0 , (nobody worked that day) ,
we need the number of terms of
300+285 + ... + 15
the left side is an AS where a = 300 , d = 15 , n = ?
when the last term is 15
15 = a + d(n1)
15 = 300  15(n1)
15 = 30015m + 15
15n = 300
n = 20 
Reiny's solution just tells us the max number of days not how many days were actually used.
We know that 15 more days were used than originally planned with the full 300.
300d= the sum of the progression