How many of the numbers between 20 and 40 are prime numbers?
A) 3
B) 4
C) 5
D) 6
E) 7
Recall that a prime number is a number that only has itself and 1 as a divisor.
This is 4 numbers which is answer B
A) 3
B) 4
C) 5
D) 6
E) 7
Recall that a prime number is a number that only has itself and 1 as a divisor.
- Remove all the evens since the are divisible by 2 (20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40)
- Remove all the remaining numbers divisible by 3 (21, 24, 27, 30, 33, 36, 39)
- Remove all the remaining numbers divisible by 5 (25, 35)
This is 4 numbers which is answer B