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3 years ago

Thuy rolls a number cube 7 times. which expression represents the probability of rolling a 4 exactly 2 times?

2 answers:

6 0

The result of rolling a number cube 7 times is a 7-digit number composed of digits 1,2,3,4,5 and 6 so that digits can repeat. The total number of possibilities is 6^7.

The number of possibilities where 4 appears exactly two times is 5^5*(7!-6!/2).
5^5 is the number of 5-digits numbers composed of digits 1,2,3,5 and 6 so that digits can repeat.
7! is the number of permutations of digits 1,2,3,4,4,5 and 6.
6! is the number of permutations of digits 1,2,3,{4,4},5 and 6.
We don't want to subtract all numbers where digits 4 appear side by side. That's why we must divide 6! by 2.

Finally, the probability is P=5^5(7!-6!/2)/7^7

mel-nik [20]3 years ago

5 0

Answer:

The answer is C I just took the test!!!!!!!

Step-by-step explanation:

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aivan3 [116]

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They are b and c.

Step-by-step explanation:

Let's simplify each expression:

a. b+2 (b+2b)

= b + 2b + 4b = 7b.

b. 3b + b = 4b.

c. 2(2b) = 2 * 2b = 4b.

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Varvara68 [4.7K]

I assume there are some plus signs that aren't rendering for some reason, so that the plane should be $x+y+z=1$ .

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melomori [17]

Answer: 15

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Remember $c^{2}$ should always be the hypotenuse or the longest side.

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