0
$\begingroup$

Three standard dice are rolled and the numbers thrown are added. what is the probability of getting a sum of 15?

$\endgroup$
  • 2
    $\begingroup$ How would you approach this question? Do you have any solution-plan in mind? $\endgroup$ – Studentmath Apr 23 '14 at 11:37
  • $\begingroup$ Unfortunately not. $\endgroup$ – Aspiring Mathlete Apr 23 '14 at 12:02
3
$\begingroup$

I don't see any easier way than going over all options and summing the probabilities:

Probability $\frac{3!}{6^3}=\frac{1}{36}$:

4,5,6

Probability $\frac{3}{6^3}=\frac{1}{72}$:

3,6,6

Probability $\frac{1}{6^3}=\frac{1}{216}$:

5,5,5

All together, you get $\frac{5}{108}$.

$\endgroup$
  • 2
    $\begingroup$ $\frac{2!}{6^3}=\frac{1}{72}$? $\endgroup$ – robjohn Apr 23 '14 at 13:24
  • $\begingroup$ $\frac{2!}{6^3} = \frac{1}{108} $ Giving you $\frac{1}{24}$ and not $\frac{5}{108}$ $\endgroup$ – User011123521 Apr 23 '14 at 13:30
  • $\begingroup$ The number of variations of 3,6,6 is $\frac{3!}{2! \cdot 1!}=3$ not 2! $\endgroup$ – callculus Apr 23 '14 at 13:52
  • $\begingroup$ @robjohn - that was a mistyping. the probability is $\frac{1}{72}$, but I wrote $2!$ instead of $3$. The final answer is true as well. $\endgroup$ – R B Apr 23 '14 at 14:44
  • $\begingroup$ @RB: I noticed that you got the right answer, so I figured it was a typo. $\endgroup$ – robjohn Apr 23 '14 at 15:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.