A die is rolled three times. The probability that the sum of three numbers obtained is 15, is equal to :
Each coefficient in the equation ax2+bx+c=0 is determined by throwing an ordinary die. Find the probability that the equation will have equal roots.
Four fair dice D1,D2,D3 and D4 each having six faces numbered 1, 2, 3, 4, 5 and 6 are rolled simultaneously. The probability that D4 shows a number appearing on one of D1,D2 and D3, is ?