Probability Question

Hi, can someone help me with this question please.

I started off by finding the different possibilities you could get if you added the results of 3 rolls: 0,2,4,5,6,7,9,10,12,15,17,20,22,25,30

That didn’t pan out well

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6377D5A1-3645-402D-9D32-8F04D17C7D7C.jpg.jpeg

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Reply 1

mqb2766

Original post by subbhy

Hi, can someone help me with this question please.
I started off by finding the different possibilities you could get if you added the results of 3 rolls: 0,2,4,5,6,7,9,10,12,15,17,20,22,25,30
That didn’t pan out well
6377D5A1-3645-402D-9D32-8F04D17C7D7C.jpg.jpeg

Youre only interested in the first three cases, so how do they arise and what combinations/probabilities give them?

Reply 2

subbhy

Original post by mqb2766

Youre only interested in the first three cases, so how do they arise and what combinations/probabilities give them?

I tried doing that but I might be missing a few combos in my list

Eg 0 + 0 + 0 = 0
0 + 0 + 2 = 2

Is there a way to tell how many I should have?

Reply 3

mqb2766

Original post by subbhy

I tried doing that but I might be missing a few combos in my list
Eg 0 + 0 + 0 = 0
0 + 0 + 2 = 2
Is there a way to tell how many I should have?

Youre on the right lines, and thinking of each of the three cases (0,2,4) as a nCr counting or a simple tree should help.

Reply 4

tonyiptony

Another line of thinking, which for the most part is the same and quicker (though need some insight).

Spoiler

I'd suggest you work along the method of #2-3 first. I think you know that there is one case missing in #2.

This now becomes a counting exercise. I hope you are well-versed with nCr (since we don't care about ordering here).