math

cheuklam

how to caculate this math in a short time??
501-287-157
thanks!

yanfaidaddy

501   =  500 + 1
-287   =  -300  +  13
-157   =  -150  -  7

   501 - 287 - 157
= 500 +1 -300 +13 -150 -7
= 500 -300 -150 +1 +13 -7
= 200 -150 +14 -7
= 57

is it OK ?!