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3 years ago

(7/8)(?)=21 please help!

Mathematics

2 answers:

alukav5142 [94]3 years ago

6 0

7/8 x = 21
7x = 21×8
7x = 168
x = 24

Inessa05 [86]3 years ago

6 0

Let's let the question mark be represented by $x$ . We get the equation $\frac{7}{8}x=21$ . We need to solve for $x$ , and we can do that by first multiplying the reciprocal of $\frac{7}{8}$ , which is $\frac{8}{7}$ . When we multiply and simplify, we get that $x=24$ . Therefore, the value of the question mark that makes the equation $\frac{7}{8}?=21$ true is $\boxed{24}$ .

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The null hypothesis is $H_0: \mu \leq 10$

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At the null hypothesis, we test if the battery life is of 10 hours or less, than is:

$H_0: \mu \leq 10$

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We have the standard deviation for the sample, so the t-distribution is used to solve this question

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In which X is the sample mean, $\mu$ is the value tested at the null hypothesis, s is the standard deviation and n is the size of the sample.

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This means that $\mu = 10$

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This means that $n = 45, X = 10.5, s = 1.8$

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Test statistic t = 1.86.

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