SOLUTION: The average of four numbers is 67. If three of these numbers are 56, 87, and 72, what is the fourth number?

Algebra.Com
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): You can put this solution on YOUR website!

let the fourth number be
if the average of four numbers is , and if three of these numbers are , , and , we have






answer: the fourth number is



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
---------
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.
RELATED QUESTIONS

The average of four numbers is 67 three of these numbers are 67 87 72 what is the fourth... (answered by stanbon,macston)
The average of four numbers is 98. If three of the numbers are 86, 87, and 91, what is... (answered by checkley71)
The average of four numbers is 98. If three of the numbers are 86, 87, and 91, what is... (answered by Alan3354,richwmiller)
the average of four numbers is 98 if three of the numbers are 86 87 and 91 what is the... (answered by ikdeep)
If the average of four numbers is 25, and three of the numbers are 24, what is the fourth (answered by oscargut)
what is the average number between these numbers 87, 81,and 88 of exactly... (answered by Alan3354)
the average of four numbers is 27. if three of the numbers are 25,33,and 37 what is the... (answered by sachi)
the average of four numbers is 638.4 the first three numbers are 216,159.8,301.25. what... (answered by stanbon)
the average of eight number is 56.three of the numbers are 49, 57 & 72.what are the... (answered by Cromlix)