Answer:
probability that he or she will answer at least 4 problems correctly = 0.5
Step-by-step explanation:
probability that he or she will answer at least 4 problems correctly is given as;
P (at least 4 correctly) = P (exactly 4 correctly) + P (all 5 correctly)
Since there are 10 problems. 4 is from the 7 problems chosen and 1 is from the 3 problems we can't figure out. Thus, P(exactly 4 correctly) = 7C4 x 3C1
Thus, P (at least 4 correctly) = [ (7C4) x (3C1) ] / (10C5)] + [(7C5)/(10C5)]
= [(35 x3)/252 ] + [21/252]
= [ 105/252 ] + [ 21/252 ]
= 126 / 252
= 0.5
