The average of 20, 60 and 180 is twice the average of 10, 30, and which of the following ?
1)10
2)30
3)60
4)90
5)180
Please assist with above problem.
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alanforde800Maximus
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For the average of 20, 60, and 180 to be twice the average of 10, 30, and x, the SUM of 20, 60, and 180 must be twice the SUM of 10, 30, and x.alanforde800Maximus wrote:The average of 20, 60 and 180 is twice the average of 10, 30, and which of the following ?
1)10
2)30
3)60
4)90
5)180
Sum of 20, 60 and 180 = 20+60+180 = 260.
Since this sum must be twice the sum of 10, 30 and x, we get:
260 = 2(10+30+x)
130 = 10+30+x
x = 90.
The correct answer is D.
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Another approach:alanforde800Maximus wrote:The average of 20, 60 and 180 is twice the average of 10, 30, and which of the following ?
A) 10
B) 30
C) 60
D) 90
E) 180
We have list A: 20, 60 and 180
...and list B: 10, 30, x
20 is two times 10,
and 60 is two times 30
Since the average of list A is two times the average of list B, then it must also be the case that 180 is two times x
So, x = 90
Answer: D
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