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SCORPION-xisa [38]
3 years ago
5

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

Mathematics
2 answers:
Nady [450]3 years ago
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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Which factorization is incorrect? 1) x3 + 5x2 + 4x + x2 + 5x + 4 = (x + 4)(x + 1)2 2) 4d3 – 4d2 – 9d + 9 = (d – 1)(2d – 3)2 3) 2
Andru [333]

Answer:

The second option is the incorrect:

2) 4d3 – 4d2 – 9d + 9 = (d – 1)(2d – 3)^2

Step-by-step explanation:

Let's check each one of the factorizations:

1) x3 + 5x2 + 4x + x2 + 5x + 4 = (x + 4)(x + 1)^2

(x + 4)(x + 1)^2 = (x + 4)(x2 + 2x + 1) = x3 + 6x2 + 9x + 4

x3 + 5x2 + 4x + x2 + 5x + 4 = x3 + 6x2 + 9x + 4

This one is correct.

2) 4d3 – 4d2 – 9d + 9 = (d – 1)(2d – 3)^2

(d – 1)(2d – 3)^2 = (d - 1)(4d2 - 12d + 9) = 4d3 - 16d2 + 21d - 9

4d3 – 4d2 – 9d + 9 = 4d3 - 16d2 + 21d - 9

This one is incorrect.

3) 27h3 – 8k3 = (3h – 2k)(9h2 + 6hk + 4k2 )

(3h – 2k)(9h2 + 6hk + 4k2 ) = 27h3 - 8k3

This one is correct.

4) 64 – 9t2 = (8 + 3t)(8 – 3t)

(8 + 3t)(8 – 3t) = 64 - 9t2

This one is correct.

So the incorrect option is the second one.

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3 years ago
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