Question

How many four-digit numbers abcd exist such that a is even, b is divisible by 5, c is prime, and d is odd?

Answer 1

a = 2 4 6 8
b = 0 5
c = 2, 3, 5, 7
d = 1, 3, 5, 7

4 choices for a
2 choices for b
4 choices for c
4 choices for d

Mulitply to find how many 4 digit numbers exist under these conditions.

Answer 2

there are 4 even digits

only 1 digit, 5 , is divisible by 5
(although you could make an argument for 0)

1, 3, 5 , 7 or four digits are prime

1,3,5,7,9 or 5 digits are odd

so 4*1*4*5 = 80

Answer 3

I agree with Damon, I was thinking about zero and in 10 , 20 , etc.

Answer 4

I got 80 to thanks Damon and Dr Jane