# Math

posted by
**Joy**
.

I am lost, need to know how to do these types of problems.

How many one-to-one correspondences are there between the sets {a,b,c,d}and{1,2,3,4}if in each correspondence

A. a and c must correspond to even numbers

B. b must correspond to 3?

C. b must correspond to 3 and d to 4?