Answer:
12
Step-by-step explanation:
There are 4×3 = 12 ways that two of the four elements can be mapped to the two elements of the smaller set. Here's a list of the 12 possible functions:
{(a, 1), (b, 2}}, {(a, 2), (b, 1)}, {(a, 1), (b, 3)}, {(a, 3), (b, 1)},
{(a, 1), (b, 4)}, {(a, 4), (b, 1)}, {(a, 2), (b, 3)}, {(a, 3), (b, 2)},
{(a, 2), (b, 4)}, {(a, 4}, (b, 2)}, {(a, 3), (b, 4)}, {(a, 4), (b, 3)}
