+79 The mean of a set of 4 numbers was 18. When a 5th number was added to the set, the mean dropped to 16. What was the number added to the set?
Can somebody walk me through?
Answer: 8
What I want to know: the steps to get 8
What I did:
18 18 18 18
(18 - 16) + (18 - 16) + (18 - 16) + (18 - 16) = 8
8 +2 = 10
Where did I go wrong, and if you can't make sense of what I did, can you explain where I went wrong and how you would do it?
(and give me tips for the ISEE? thank you!)
+33616 Mean of the set of four numbers:
(x1 + x2 + x3 + x4)/4 = 18
Multiply both sides by 4, so
x1 + x2 + x3 + x4 = 4*18 ...(1)
Mean of the five numbers
(x1 + x2 + x3 + x4 + x5)/5 = 16
Multiply both sides by 5, so
x1 + x2 + x3 + x4 + x5 = 5*16 ...(2)
Replace x1 + x2 + x3 + x4 in (2) by using (1)
4*18 + x5 = 5*16
Subtract 4*18 from both sides
x5 = 5*16 - 4*18
x5 = 80 - 72
x5 = 8
