The number of integers from 1 to 100 which are neither divisible by 3 ...
Solution:
To find the number of integers from 1 to 100 which are neither divisible by 3 nor by 5 nor by 7, we use the principle of inclusion and exclusion.
Step 1: Find the number of integers divisible by 3, 5 and 7 separately.
The number of integers divisible by 3 from 1 to 100 is 33. (Divide 100 by 3 and take the floor value).
The number of integers divisible by 5 from 1 to 100 is 20. (Divide 100 by 5 and take the floor value).
The number of integers divisible by 7 from 1 to 100 is 14. (Divide 100 by 7 and take the floor value).
Step 2: Find the number of integers divisible by 3 and 5, 5 and 7, 3 and 7 separately.
The number of integers divisible by both 3 and 5 from 1 to 100 is 6. (Divide 100 by 15 and take the floor value).
The number of integers divisible by both 5 and 7 from 1 to 100 is 2. (Divide 100 by 35 and take the floor value).
The number of integers divisible by both 3 and 7 from 1 to 100 is 4. (Divide 100 by 21 and take the floor value).
Step 3: Find the number of integers divisible by 3, 5 and 7.
The number of integers divisible by 3, 5 and 7 is 0.
Step 4: Apply the principle of inclusion and exclusion.
The number of integers from 1 to 100 which are neither divisible by 3 nor by 5 nor by 7 is:
= Total number of integers - (Number of integers divisible by 3 + Number of integers divisible by 5 + Number of integers divisible by 7)
+ (Number of integers divisible by both 3 and 5 + Number of integers divisible by both 5 and 7 + Number of integers divisible by both 3 and 7)
- Number of integers divisible by 3, 5 and 7
= 100 - (33 + 20 + 14) + (6 + 2 + 4) - 0
= 45
Therefore, the correct answer is option (c) 45.
The number of integers from 1 to 100 which are neither divisible by 3 ...
I think ans is 67