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What is the value of 10 percent of y?

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Source: — Data Sufficiency |

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by Brent@GMATPrepNow » Mon Jul 24, 2017 11:06 am
jjjinapinch wrote:What is the value of 10 percent of y?

(1) 5 percent of y is 60.
(2) y is 80 percent of 1,500.

Official Guide question
Answer: D
Target question: What is the value of 10 percent of y?

Statement 1: 5 percent of y is 60
If 5 percent of y is 60, then 10 percent of y is 120
Since we can answer the target question with certainty, statement 1 is SUFFICIENT

Aside: we can keep going with this logic.
For example, if 5% of y is 60 then 0.5% of y is 6
and 50% of y is 600
and 15% of y is 180
and 20% of y is 240
and 25% of y is 300
etc...

Statement 2: y is 80 percent of 1,500
So, y = 80/100 of 1500
In other words, y = (0.8)(1500)
Since we COULD determine the value of y, we COULD then find the value of 10 percent of y
Since we COULD answer the target question with certainty, statement 2 is SUFFICIENT

Answer: D

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Brent
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by [email protected] » Mon Jul 24, 2017 5:32 pm
Hi jjjinapinch,

This DS question is designed with some great concept 'shortcuts' - meaning that you don't need to do any actual math to answer this question (as long as you recognize the concepts involved).

We're asked for the value of 10% of Y.

1) 5% of Y = 60

This is one variable with one equation (with nothing special - such as exponents), meaning that you CAN solve it (and there will be just one answer). If you chose to solve it, you'd have...

.05(Y) = 60
Y = 1200

As it is, you don't have to do that work if you recognize the Algebra concept involved here.
Fact 1 is SUFFICIENT

2) Y is 80% of 1500

Again, we have the same concept as in Fact 1 (above) - one variable and one equation.... so we know it's SUFFICIENT. Here's the proof though:

Y = (.8)(1500)
Y = 1200
Fact 2 is SUFFICIENT

Final Answer: D

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Rich
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