Question

how many natural numbers are there between 1to 200 which they are exatly divisible by 3, 9 and 27​

Answer 1

Answer:

Number divisible by 3

3,6,9……………198

Using the formula of finding nth term in an Arithmetic Progression

an= a+ (n-1)d ….. (1)

where an: nth term, a:first term n:number of terms d:common difference

198=3+(n-1)3

=> n=66

Number divisible by 7

7,14,………………………196

196=7+(n-1)7 [from (1)]

n=28

Number divisible by 21

21,42…………………….189

189= 21+ (n-1)21 [from(1)]

n=9

Number divisible by 3 or 7 [not by 21] = 66+28–9=85… Ans

Hope it helps!