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In article <1167557963.377775.165150@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
john <johnboy98105@xxxxxxxxx> wrote:
>These ones either I got them wrong or guessed and got them right.
>
>Q1:
>
>Average (arithmetic mean) of Test Scores in Class R
>Average scores for the boys 90
>Average scores for the girls 81
>Average scores for the class 84
>
>What is greater? The number of boys in the class who took the test or
>The number of girls in the class who took the test.
>
>A1: the number of girls took the test is greater.
>
>I got so confused on this... Some tips will be welcome
>
Formally, if there are b boys and g girls in the class we have, by
equating the total scores we get:
90 b + 81 g = 84 (b+g)
6b = 3g
2b = g
There are thus twice as many girls as boys in the class.
>
>
>Q2:
> x > 1
> y > 1
>
>What is greater? 1 / ( 1/x + 1/y) or 1/x + 1/y that is...
>
>a. b.
> 1 1 1
>------------------- or ------- + ------
> 1 1 x y
>------- + ------
> x y
>
>
>
>A2: Need more information to determine the relationship.
>
>
>I got this one wrong after plugging in x = 2, y = 3
>
>so i figured....
>
>a. xy b. y + x
> ---------- ----------
> x + y xy
>
> 6/5 > 5/6
>
>or if x= 2, y = 5
>
>then
> 10/7 > 7/10
>
>
>or if x = 5, y = 5
>
>then 25/10 > 10/25
>
>I can't get why you need more info to determine the relantionship..
>What's the trick here?
>
If 1/x + 1/y is less than 1, then the first quantity will be greater.
However if 1/x + 1/y is greater than 1 then the second quantity will be
greater. If you are only given the constraints that x>1 and y>1, then
1/x + 1/y might either be greater or less than 1. For example, if
x=y=3/2, then 1/x+1/y=4/3 > 1, but in the examples you tried (e.g. x=2,
y=3) you had 1/x + 1/y < 1.
--
Daniel Mayost
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