Question

How many natural numbers between 200 and 400 are there which are divisible by i) Both 4 and 5? ii) 4 or 5 or 8 or 10? A) 9,79 B) 10,80 C)10,81 D) None of these

Answer 1

i)If it should be divisible by both 4 and 5 therefore it should be divisible by 20.
therefore..
AP=220,240,260....,380
d=240-220
=20
In Ap..
l=a+(n-1)d
380=220+(n-1)20
380-220=(n-1)20
160/20=n-1
8+1=n
n=9..
Therefore there are 9 numbers which are divisible by 4 and 5 between 200 and 400