what is the number of integers from 1 to 1000 ( inclusive ) that are divisible by neither 15 nor by 20 ?
"in 1000 consecutive numbers , number of multiples of 15 = 1000 / 15 = 66 ( ignore decimals ) in 1000 consecutive numbers , number of multiples of 20 = 1000 / 20 = 50 number of multiples of 15 * 20 i . e . 300 = 1000 / 300 = 3 number of integers from 1 to 1000 that are divisible by neither 15 nor by 20 = 1000 - ( 66 + 50 - 3 ) { using the concept of sets here ) = 887 answer is a"
subtract(1000, subtract(add(divide(1000, 15), divide(1000, 20)), divide(1000, multiply(15, 20))))