# math, help

posted by
**student**
.

For this one i have no idea what formula or even how to set it up...

Tow 6-sided dice are rolled. What is the porbability that the sum of the two numbers on the dice will be greater than 9?

Notation: n1 is the number that die 1 shows, n2 is the number that die 2 shows.

Then we want to know in how many ways you can have:

n1 + n2 > 9

where:

1 <= n1 <= 6

1 <= n2 <= 6

We know that without restrictions there are 36 possibilities (both n1 and n2 can then take 6 values), so we have to divide the number of possibilities by 36.

In this case the number of possibilities is not that large and you can just count all possibilities:

n1 = 4, n2 = 6

n1 = 5, n2 = 5

n1 = 5, n2 = 6

n1 = 6, n2 = 4

n1 = 6, n2 = 5

n1 = 6, n2 = 6.

by anychance do you know of a good website where it shows a similar example of how to use this type of formula....

I think the best thing you could do is study discrete mathematics from a good textbook.

I just found this PDF file:

http://www.cs.tau.ac.il/~odedr/teaching/discrete_math_fall_2005/dmbook.pdf