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a = 5b^2 – 10b + 7

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a = 5b^2 – 10b + 7 [#permalink] New post 21 Jun 2017, 13:08
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57% (01:05) correct 42% (01:19) wrong based on 47 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] New post 04 Feb 2018, 01:19
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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] New post 18 Feb 2018, 06:06
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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.

Answer: A
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Re: a = 5b^2 – 10b + 7 [#permalink] New post 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.

Answer: A


great approach, didn't think of that
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Re: a = 5b^2 – 10b + 7 [#permalink] New post 01 Mar 2018, 05:25
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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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