Math  /  Data & Statistics

Question\begin{tabular}{|l|l|} \hline What are the chances of them adding up to 6 or 8 ? & 0.167 \\ \hline What are the chances of them adding up to a prime number? & \\ \hline What are the chances of rolling a double (same number on each die)? \\ \hline What are the chances of rolling snake-eyes twice in a row? & \\ \hline \end{tabular}

Studdy Solution

STEP 1

What is this asking? We're rolling two dice, and we want to figure out the probabilities of getting certain sums or outcomes! Watch out! Don't forget that each die has 6 sides, numbered 1 to 6, and that each roll is independent!

STEP 2

1. Prime Sum Probability
2. Double Probability
3. Snake Eyes Probability

STEP 3

Alright, let's **investigate** the prime sums!
First, let's **list** all the possible sums we can get when rolling two dice.
The smallest sum is 1+1=21 + 1 = 2 and the largest is 6+6=126 + 6 = 12, so our possible sums are 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12.

STEP 4

Now, let's **identify** the prime numbers in that list.
Remember, a prime number is a whole number greater than 1 that has only two divisors: 1 and itself.
Looking at our list, the prime sums are **2, 3, 5, 7, and 11**.

STEP 5

Time to **figure out** how many ways we can roll each of these prime sums.
We can get a sum of 2 in only one way: 1+11 + 1.
A sum of 3 can be rolled in two ways: 1+21 + 2 and 2+12 + 1.
A sum of 5 can be rolled in four ways: 1+41 + 4, 2+32 + 3, 3+23 + 2, and 4+14 + 1.
A sum of 7 can be rolled in six ways: 1+61 + 6, 2+52 + 5, 3+43 + 4, 4+34 + 3, 5+25 + 2, and 6+16 + 1.
Finally, an 11 can be rolled in two ways: 5+65 + 6 and 6+56 + 5.

STEP 6

Let's **add up** the number of ways to get a prime sum: 1+2+4+6+2=151 + 2 + 4 + 6 + 2 = 15.
Since there are 66=366 \cdot 6 = 36 total possible outcomes when rolling two dice, the probability of rolling a prime sum is 1536=512\frac{15}{36} = \frac{5}{12}.

STEP 7

Rolling doubles means both dice show the same number.
This can happen in six ways: 1+11 + 1, 2+22 + 2, 3+33 + 3, 4+44 + 4, 5+55 + 5, and 6+66 + 6.

STEP 8

With 66 favorable outcomes and 3636 total possible outcomes, the probability of rolling doubles is 636=16\frac{6}{36} = \frac{1}{6}.

STEP 9

Snake eyes means rolling two ones.
There's only one way to do this: 1+11 + 1.

STEP 10

The probability of rolling snake eyes once is 136\frac{1}{36}.
Since each roll is independent, the probability of rolling snake eyes *twice* in a row is 136136=11296\frac{1}{36} \cdot \frac{1}{36} = \frac{1}{1296}.

STEP 11

The probability of rolling a prime sum is 512\frac{5}{12}.
The probability of rolling doubles is 16\frac{1}{6}.
The probability of rolling snake eyes twice in a row is 11296\frac{1}{1296}.

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