Let N be the number of nickels. Then the number of dimes is 2N and the number of quarters is (21-N-2N) - (21-3N). The "money" equation is 5N + 10*(2N) + 25*(21-3N) = 275 cents. Simplify and solve 5N + 20N + 25*21 - 75N = 275 -50N = 275 - 25*21 N == 5. ANSWER. 5 nickel, 2*5 = 10 dimes and the rest 21 - 5 - 10 = 6 coins are quarters. CHECK. 5*5 + 10*10 + 6*25 = 275 cents. ! Correct !