Question

How many natural number between 200 and 400 are there which are divisible by both 4 and 5?

Answer 1

Answer: 9

Step-by-step explanation:

Divisible by both 4 and 5 means, divisible by 20 as 20 is the lcm of 4 and 5

First number after 200 which is divisible by 20 is 220 and last number before 400 is 380

We have to find the value of n in the arithmetic progression where a₁ =220, d = 20 and aₙ = 380

a₁ + (n-1) d =380

220 + ( n-1) 20 = 380

20n = 380 -200 180

n =9