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# a = 5b^2 – 10b + 7

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a = 5b^2 – 10b + 7 [#permalink]  21 Jun 2017, 13:08
Expert's post
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Question Stats:

62% (01:15) correct 37% (01:57) wrong based on 75 sessions

a = $$5b^2$$ – 10b + 7

 Quantity A Quantity B a b

A) Quantity A is greater.
B) Quantity B is greater.
C) The two quantities are equal.
D) The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

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Re: a = 5b^2 – 10b + 7 [#permalink]  04 Feb 2018, 01:19
2
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a = 5b^2 – 10b + 7
let b=0, so a=7
b=1, a= 2
b=-1, a=22
So Q.A is greater.
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Re: a = 5b^2 – 10b + 7 [#permalink]  18 Feb 2018, 06:06
2
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a = 5b^2 - 10b + 7
Subtract b from both sides
a - b = 5b^2 - 11b + 7
Since the coefficient of b^2 is positive the RHS is >0.

So a-b>0 --> a>b.

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Re: a = 5b^2 – 10b + 7 [#permalink]  18 Feb 2018, 23:56
gremather wrote:
a = 5b^2 - 10b + 7
Subtract b from both sides
a - b = 5b^2 - 11b + 7
Since the coefficient of b^2 is positive the RHS is >0.

So a-b>0 --> a>b.

great approach, didn't think of that
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Re: a = 5b^2 – 10b + 7 [#permalink]  01 Mar 2018, 05:25
3
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It's a good question.

First need to simplify and then plugin as below:

Quantity A: $$5b^2$$ – 10b + 7
Quantity B: b

So, we can add 10b on both Quantities, because the inequality will not change i.e:

Quantity A: $$5b^2$$ + 7
Quantity B: 11b

Now, don't plugin -ve values, because Quantity A will always greater (being positive). Also in 0, Quantity A will be greater.
Finally, just check for positive values. You will see Again, Quantity A always greater.
For positive values, just plugin one value from (0 - 1) and other one from any value greater than 1.

Choice Choice A is correct.
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Re: a = 5b^2 – 10b + 7   [#permalink] 01 Mar 2018, 05:25
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