Answer:
5%
Step-by-step explanation:
so, for 3 questions he has a 1 in 4 chances to get it right.
4³ chances, so a 1/4³ probability.
and he has one other question with a 3 in 4 chance to get it wrong.
a 3/4 probability.
that is in total
1/4³ × 3/4 = 3/4⁴
and now we have 4 over 3 combinations as possibilities to get 3 right and 1 wrong.
that is 4! / (3! × (4-3)!) = 4
so our total probability is
4 × 3/4⁴ = 3/4³ = 3/64 ≈ 0.05 = 5%
in other words, the expected quote for him to achieve that result is in 5 out of 100 (or 1 out of 20) attempts.
