Question 1131017
This problem requires the use of the Binomial Probability formula
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Probability (P) (k successes out of n trials) = nCk * p^k * (1-p)^(n-k), where nCk = n!/(k! * (n-k)!), p is the probability of a success
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P for guessing an answer correctly is 1/4 
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P for guessing an answer incorrectly is 1 - 1/4 = 3/4
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P ( at least 1 success in 15 trials) = 1 - P(0 successes in 15 trials) = 1 - 15C0 * (1/4)^0 * (3/4)^(15-0) = 1 - 0.01 = 0.99
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Note "at least one of them right" means 1 or 2 or 3 or 4 ...... or 15
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