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2 years ago

Mr. Akika has 30 24-cent and 33-cent stamps all told. The stamps are worth $8.91. How many of each kind of stamp does he have?

Mathematics

1 answer:

riadik2000 [5.3K]2 years ago

7 0

Answer:

24-cent: 11
33-cent: 19

Step-by-step explanation:

I find it easiest to solve these using the variable to represent the number of the most-expensive item. Let x represent the number of 33-cent stamps. Then the total value (in cents) is ...

33x +24(30 -x) = 891

9x = 171 . . . . . . . . . . . . . subtract 24(30), collect terms

x = 19 . . . . . . . . . . . . divide by 9

30-x = 11 . . . . . . . find the number of 24-cent stamps

Mr. Akika had 11 24-cent stamps and 19 33-cent stamps.

_____

Additional comment

You seem to have several of these to solve. They all have a similar solution.

If we let x represent the number of higher-value items, N, the total number of items, V the total value, and v1 and v2 the individual values (v2 > v1), the equation is ...

v2(x) +v1(N -x) = V

x(v2 -v1) = V -v1·N

x = (V -v1·N)/(v2 -v1) . . . . generic solution

Using this formula in the problem here, we find ...

x = (891 -24(30))/(33 -24) = 171/9 = 19 . . . as above

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Answer:

The Chi-square test of independence

Step-by-step explanation:

The answer to this question is the Chi-square test of independence because it is what is used to determine the existence of an association between nominal/categorical variables. This test is non parametric in nature and it can also be called the chi square test of association.

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3 years ago

A system of equations is shown below.

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Given:

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To find:

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Solution:

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Therefore, the correct option is A.

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3 years ago

Which equation represents a line parallel to the line shown on the graph? On a coordinate plane, a line goes through (0, 8) and

dezoksy [38]

Answer:

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Step-by-step explanation:

Find the slope of the line that goes through (0, 8) and (2, 0):

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2 years ago

What is the common denominator 2 1/3+1/2?

nirvana33 [79]

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3 years ago

"A manufacturer of automobile batteries claims that the average length of life for its grade A battery is 55 months. Suppose the

STALIN [3.7K]

Answer:

$\\ P(z>-2) = 0.97725$ or P(x>49) is about 97.725% (or being less precise 97.5% using the empirical rule).

Step-by-step explanation:

We solve this question using the following information:

We are dealing here with normally distributed data, that is "the frequency distribution of the life length data is known to be mound-shaped".
The normal distribution is defined by two parameters: the population mean ( $\\ \mu$ ) and the population standard deviation ( $\\ \sigma$ ). In this case, we have that $\\ \mu = 55$ months, and $\\ \sigma = 3$ months.
To find the probabilities, we have to use the standard normal distribution, which has $\\ \mu = 0$ and $\\ \sigma = 1$ . The probabilities for this distribution are collected in the standard normal table, available in Statistics books or on the Internet. We can also use statistics programs to find these probabilities.
For most cases, we need to use the cumulative standard normal table, and for this we have to previously "transform" a raw score (x) into a z-score using the next formula: $\\ z = \frac{x - \mu}{\sigma}$ [1]. A z-score tells us the distance from the mean that a raw score is from it in standard deviations units. If this value is negative, the raw score is below the mean. Conversely, a positive value indicates that it is above the mean.
The cumulative standard normal table is made for positive values of z. Since the normal distribution is symmetrical around the mean, we can find the negative values of z using this formula: $\\ P(z$ [2].

Having all this information, we can solve the question.

<h3>The percentage of the manufacturer's grade A batteries that will last more than 49 months</h3>

First Step: Use formula [1] to find the z-score of the raw score x = 49 months.

$\\ z = \frac{49 - 55}{3}$

$\\ z = \frac{-6}{3}$

$\\ z = -2$

This means that the raw score is represented by a z-score of $\\ z = -2$ , which tells us that it is two standard deviations below the population mean.

Second Step: Consult this value in the cumulative standard normal table for z = 2 and apply the formula [2] to find the corresponding probability.

For a z = 2, the probability is 0.97725.

Then

$\\ P(z$

$\\ P(z2)$

But we are not asked for P(z<-2) but for P(z>-2) = P(x>49). This probability is the complement of the previous result, that is

$\\ P(z>-2) = 1 - P(z$

$\\ P(z>-2) = 1 - 0.02275$

$\\ P(z>-2) = 0.97725$

That is, the "percentage of the manufacturer's grade A batteries will last more than 49 months" is

$\\ P(z>-2) = 0.97725$ or about 97.725%

A graph below shows this result.

Notice that if we had used the 68-95-99.7 rule (also known as the empirical rule), that is, in a normal distribution, the interval between one standard deviation below and above the mean contains, approximately, 68% of the observations; the interval between two standard deviations below and above the mean contains, approximately, 95% of the observations; and the interval between three standard deviations below and above the mean contains, approximately, 99.7% of the observations, we could have concluded that 2.5 % of the manufacturer's grade A batteries will last less than 49 months, and, as a result, 1 - 0.025 = 0.975 or 97.5% will last more than 49 months.

We can conclude that with a less precise answer (but faster) because of the symmetry of the normal distribution, that is, 1 - 0.95 = 0.05. At both extremes we have 0.05/2 = 0.025 or 2.5% and we were asked for P(x>49) = P(z>-2) (see the graph below).

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3 years ago