>>237

sum binomial(15, i)*4^(15-i) from i = 5 to 15 = 5012015501
5 * 5012015501 = 25060077505

sum binomial(15, i)*binomial(15-i, j)*3^(15-i-j) from j = 5 to 15-i from i = 5 to 10 = 323173994
binomial(5, 2) * 323173994 = 3231739940

binomial(15, 5) * binomial(10, 5) = 756756

25060077505 - 3231739940 + 756756 = 21829094321

5^15 = 30517578125

21829094321 / 30517578125 = 0.715295762710528