Question

how many numbers are there between 100and 1000 which are divisible by 5

Answer 1

105,110,115......995
it is an AP so
995 = 105+(n-1)*5
890=5n-5
895=5n
n=199

Answer 2

100,105,110............1000
a=100
an=1000
d=5
n=?
an=a+(n-1)×d
1000=100+(n-1)×5
1000=100+5n-5
1000=95+5n
1000-95=5n
905÷5=n
n=181