Question 1197150: The average of four numbers is 67. If three of these numbers are 56, 87, and 72, what is the fourth number?
Found 3 solutions by ewatrrr, MathLover1, greenestamps:
Answer by ewatrrr(24785)   (Show Source):
You can put this solution on YOUR website!
Hi
The average of four numbers is 67.
If three of these numbers are 56, 87, and 72,
what is the fourth number? Let x represent the 4th number
Question States:
(56 + 87 + 72 +x)/4 = 67
56 + 87 + 72 + x= 4*67
x = 53
Checking answer:
(56 + 87 + 72 + 53)/4 = 67 checks.
Wish You the Best in your Studies.
Answer by MathLover1(20850)  (Show Source):
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
An alternative method for solving a problem like this, involving the average of a set of numbers that are close together, is to look at the "overs" and "unders" for each of the numbers.
In this example, compared to the average of 67, the given numbers are
56: -11
87: +20
72: + 5
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sum: +14
Together, the three known numbers are +14 compared to the average; the fourth number has to be -14 compared to the average.
ANSWER: 67-14 = 53
Note with this example, where the numbers themselves are small, there is little if any advantage of this method over the standard method shown by the other tutors. But there are occasions where this method is much faster.
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