5 and 7
There are two : 5 and 7.
3 units
18
2 3 5 7 11 13
11.. 7+4=11 and 15-4=11
-7
7
11
7 11.
5 and 7
18
3 units
There are two : 5 and 7.
The numbers 5, 7, 11 and 13 are prime (including the boundaries).
3+5+7+9+11=35
A number is divisible by 7 if it is a multiple of 7, so to figure it out, start listing multiples of 7. 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, ... On this list there are 11 numbers that are between 11 and 90. The answer is 11 numbers between 11 and 90 are divisible by 7.