Question

how many 3 digits no' s are divisible by 7 using AP​

Answer 1

A.P. between 100 and 999 which are divisible by 7 are.....

105,112......994

a = 105

d = 112-105 = 7

tn = a + (n-1)d

994 = 105 +(n-1)7

994-105 = (n-1)7

889 = (n-1)7

889/7 = n-1

n = 127 + 1

n = 128

Hence, numbers which are divisible by 7 = n = 128