Pramod can finish three-eighths of a job in 15 days. Qadir works at one-third of Pramod's daily output. How many days would Qadir take to finish the whole job on his own?

If three-eighths takes Pramod 15 days, the whole job takes him $15\times 8/3=40$ days, so he does 1/40 of it a day. Qadir does a third of that, 1/120 a day, and needs 120 days. 40 days is Pramod's own figure for the whole job, not Qadir's. 45 days trebles the 15 days, but those 15 days cover only three-eighths of the job. 360 days applies the one-third twice, once in scaling the job up and again in scaling the rate down.