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According to Sturge's rule, number of classes or bins recommended to construct a frequency distribution is k ≈ 7
Sturge's Rule: There are no hard and fast guidelines for the size of a class interval or bin when building a frequency distribution table. However, Sturge's rule offers advice on how many intervals one can make if one is genuinely unable to choose a class width. Sturge's rule advises that the class interval number be for a set of n observations.
Given,
n = 66
We know that,
According to Sturge's rule, the optimal number of class intervals can be determined by using the equation:

Here, n is equal to 66 and by substituting the value to the equation we get:

k = 7.0444
k ≈ 7
Learn more about Sturge's rule here: brainly.com/question/28184369
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Answer:
x(6 + 15y)
Step-by-step explanation:
In this instance, you can divide by a factor of x.
6x/x = 6
15xy/x = 15y
Therefore, we are left with 6 + 15y.
First, find how much he paid by tire.
To do so, divide what he paid by how many tires he bought like this :
240$ / 12 = 20$ per tire
Then, calculate how much he sells each tire.
To do so, start by calculating how much he paid for 3 tires:
20$ x 3 = 60$
This is the price he sells 2 tires for, therefore :
60$ / 2 = 30$
he sells his tires 30$ each.
Finally, you have to calculate the profit he made by selling 12.
We already know how much it cost, so you need to find how much money he gets selling them :
12 tires x 30$ = 360$
To find the profit, take off the amount he paid from the amount he made :
360$ - 240$ = 120$
There you go!