Dice Problem

Four dice are rolled. The number of ways in which at least one die shows 3, is

625 1296 671 1256

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2 solutions

Melissa Quail
Aug 31, 2015

The number of possible outcomes is 6 4 6^4 because there are 6 possible numbers on each die and there are 4 dice so 6 x 6 x 6 x 6 possible outcomes. The number of outcomes without a three on any of the dice is 5 4 5^4 because there are five possible outcomes for each die if 3 is not on any of them. So subtracting this from the total number of outcomes leaves 6 4 5 4 = 671 6^4 - 5^4 =\boxed{671} outcomes where a three is on at least one of the dice.

Ariella Lee
Dec 8, 2015

Here is a way by PIE.

Number of ways you can have one die show up 3 3 is ( 4 1 ) × 6 3 \binom{4}{1}\times 6^{3} because you have 4 4 options for which die is 3 3 and each of the other 3 3 die have 6 6 possible numbers. Similarly, the number of ways two dice show up 3 3 is ( 4 2 ) × 6 2 \binom{4}{2}\times6^{2} , three dice is ( 4 3 ) × 6 \binom{4}{3}\times6 , and four dice is just 1 1 .

The number of ways for two dice is counted ( 2 1 ) = 2 \binom{2}{1}=2 times, so subtract it once. The number of ways for three dice is counted ( 3 1 ) ( 3 2 ) = 0 \binom{3}{1}-\binom{3}{2}=0 times, so add it once. The number of ways for four dice is counted ( 4 1 ) ( 4 2 ) + ( 4 3 ) = 2 \binom{4}{1}-\binom{4}{2}+\binom{4}{3}=2 times, so subtract it once.

Total: ( 4 1 ) 6 3 ( 4 2 ) 6 2 + ( 4 3 ) 6 ( 4 4 ) = 671 \binom{4}{1}6^{3}-\binom{4}{2}6^{2}+\binom{4}{3}6-\binom{4}{4}=\boxed{671}

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