In the month of March, Dalip earned on an average ₹501 per day. For the first 18 days, his average earning was ₹495 and, for the last 15 days, his average earning was ₹505. On 18^th March, he earned ₹50 more than that earned on 17^th March. How much (in ₹) did he earn on 18^th March?

502

Total earning of Dalip in march = 501 x 31 =15531

For 1st 18 days he earns = 495 x 18 = 8910

for last 15 days he earns = 505 x 15 = 7575

As 17th day and 18th falls in both first 18 days and last 15 days 

Sum of His earning on 17th and 18t march = 8910 + 7575 -15531 = 954

Lets assume his earning on 18th march is x

So, his earning on 17th march = x - 50

From above,  x + x-50 = 954

∴ His Earning on 18th Day = x = 502