The formula
, where r! is defined as 1*2*3*...r
provides the total number of combinations for forming groups of r items from a collection of n items.
For instance, with 10 items, there are C(10,6) possible ways to create groups of 6 from these 10 objects.
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Choosing 4 individuals from a total of 12 can be accomplished in:
many different ways.
All unique groupings of 4 individuals, including the husband and wife pair, can be computed as C(10, 2) ways, since we only consider the potential selections of 2 from 10 individuals to form a group of 4.

Consequently, the probability that both the husband and wife are selected is 45/495=0.09
Part 2)
The chance that one gets selected while the other does not =
P(husband selected, wife not selected) + P(wife selected, husband not selected)
These two scenarios are precisely equal, so it suffices to compute one.
Let's analyze the scenario: husband chosen, wife not selected.
Assuming the husband is selected, we need to determine the possible formations of 3 from the 11 total excluding the wife=10 individuals.
This results in:

Hence,
P(husband selected, wife not selected)=120/495=0.24
Thus, the overall probability that one is picked while the other is not =
P(husband selected, wife not selected) + P(wife selected, husband not selected) =
0.24+0.24=0.48
Result:
A) 0.09
B) 0.48