Question

The number of integers from 1 to 20 which are divisible by 3 or 5
A.56
B.40
C.24
D.8

Answer 1

Hint: We are going to find the multiples of 3 and 5 here. Find multiples of 3 and 5 between 1 to 20 then write the count.

Complete step-by-step answer:
Given, there are numbers from 1 to 20 which are divisible by 3 or 5
Consider the multiples of 3 that lie between 1 and 20 which are {3,6,9,12,15,18}
And consider the multiples of 3 that lie between 1 and 20 which are {5,10,15,20}
Now we can see that 15 is common in both the sets. Hence, would be considered only once.
Which implies the number of integers from 1 to 20 which are divisible by 3 or 5 are given by {2,6,9,10,12,15,18,20} which contains 8 numbers.
Therefore, option D. 8 is the required solution.

Note: One should observe the common elements carefully as they may be counted more than once. We should have knowledge of multiples of numbers and divisibility rule.