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polet [3.4K]
4 years ago
8

The average of four numbers is 90.Three of them are 138,40,and 102 find the fourth number

Mathematics
2 answers:
Ymorist [56]4 years ago
8 0

Answer:

x=80

Step-by-step explanation:

To find the average, we take the numbers, add them up.  Then divide by the number of terms we added.

Let x= the unknown number

The average =90

Average = (138+40+102+x)/4

90 = (138+40+102+x)/4

Multiply by 4 on each side

90*4 =(138+40+102+x)/4 *4

360 = (138+40+102+x)

Combine like terms

360 = 280 +x

Subtract 280 from each side

360-280 = 280+x-280

80 =x


kkurt [141]4 years ago
8 0
<h2>Steps</h2>

So remember that the average formula is \frac{\textsf{sum of all the numbers}}{\textsf{how many numbers there are}} . With the info that we are given, our equation is (Let x = fourth number):

\frac{138+40+102+x}{4}=90

From here we can solve for x. Firstly, add up the numerator:

\frac{280+x}{4}=90

Next, multiply both sides by 4:

280+x=360

Lastly, subtract both sides by 280:

x=80

<h2>Answer</h2>

<u>In short, the fourth number is 80.</u>

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