Answer:
0.24
Step-by-step explanation:
This is a form of a Bernoulli trial problem.
The probability of finding a couple that do not buy gift for each other is 35/100 = 0.35
The probability of finding a couple who are gift buyers is 1 - 0.35 = 0.65
Now to compute the probability, by using the Bernoulli trial:
P(4) = nCr (p)^n (q)^n - 1
P(4) = 10C4 * 0.35^4 * 0.65^6
P = 0.24