Guide 6 Page 115 Chapter 7

[kpkanupriyakhmi]

Q 3:-
Abe's Quiz scores are.....
Could not understand the concept of too low in the explanation

[n00bpron00bpron00b]

Abe's scores in 4 tests : 62,68,74,68
Ben's scores in 2 tests : 66,70

Quantity A:

Score Abe needs on his fifth test to raise his average to 70

Avg = (Sum)/total

70 = (62+68+74+68+x)/5
where x = unknown score in the 5th test

70=(272+x)/5
350=272+x
x=78

Score Abe needs on his 5th test to get his overall average to 70 = 78

Quantity B:

Score Ben needs on his third test to raise his average to 70

Avg = (Sum)/total

70 = (66+70+x)/3
where x = unknown score in the 3rd test

70=(136+x)/3
210=136+x
x=74

Score Ben needs on his 3rd test to get his overall average to 70 = 74

Quantity (A) is greater

[tommywallach]

We could also this question with residuals. Think of 70 as the balance point of a scale, and the data points as putting WEIGHT on either side of the scale.

62 puts a weight of 8 to the left
68 puts a weight of 2 to the left
74 puts a weight of 4 to the right
68 puts a weight of 2 to the left

This makes 12 to the left total, and 4 to the right, ending up at 8 to the left. This means we need a point that is 8 to the RIGHT to balance out, so the final term will be 78.

With Ben:

66 is 4 to the left
70 is at the balance point, so has no effect

So we need something 4 to the right to balance out, so the final term will be 74.

-t