PLEASE EXPLAIN DS#79 IN 12TH EDITION REVIEW BOOK (PG#315)

[clinton]

I need help!!!

[neerajkumar1_1]

please post the problem....

[Geva@EconomistGMAT]

I need help!!!

Two options to buy a computer:
p1 dollars +sales tax of t1 percent,
Or
P2 dollars + sales tax of t2 percent.
Is the total cost of the computer greater in the first case than in the second?

(1) t1>t2
(2) p1t1 > p2t2

[Geva@EconomistGMAT]

I need help!!!

Two options to buy a computer:
p1 dollars +sales tax of t1 percent,
Or
P2 dollars + sales tax of t2 percent.
Is the total cost of the computer greater in the first case than in the second?

(1) t1>t2
(2) p1t1 > p2t2

the solution method is just as the OG says - plug in numbers. The secret is to make the separation between the numbers t1 and t2, and what the numbers stand for (i.e. percents).

For stat. (1), we have no clue what's the price of the computers. Plug in t1=10, t2=5, for example, but the final result will depend on the cost of the computers:
If P1=$100, then P1+tax will equal 100 + 10% of 100 = $110
If P2 is then also equal to $100, then P2+tax will equal 100+5% of 100 = $105, and A>B
But if P2 costs $200, then P2+tax will equal 200+5% of 200 = $210, and A<B.
Insufficient.

(2) This one is trickier, but remember:
when you're plugging in t1=10, you're not plugging in t1=10% - just t1=10.
Thus, using our original plug ins:
p1*t1 = 100*10 = 1000 (note - we're multiplying by t1=10, not 10 percent - that's what the statement says, so that's what we stick to)
p2*t2 = 100*5 = 500
we've already seen that in this case the prices are $100 and $105, and A>B.

for a second plug in, try to break this pattern while still conforming to the statement: you want a small P1 and and a large t1, so that P1*t1 is still greater than p2*t2, but the move to percents will result with a small price for A.
Take p1=10 and t1 = 100, so that p1*t1 is still 10*100 = 1000 (which is greater than p2*t2=500, satisfying the statements)
But the minute we move to percents, we get that the price of computer A is now $10 + 100% of 10 = $10+$10 = $20 - much smaller than the $105 price of B. A<B, so stat. (2) is insufficient.

since t1=100 is greater than t2=5, this case also satisfies stat. (1), meaning that both statements combined still allow both A>B and A<B - answer is E.

[bynddrvn]

Thank you!

I have one follow up question for the GMAT experts.

Just to be clear, the Official Guide 12th edition is misprinted, yes? In my book on p315 it says P1(1+ T1/0)? I believe the equation should be P1(1+ T1/100).

[Brent@GMATPrepNow]

Thank you!

I have one follow up question for the GMAT experts.

Just to be clear, the Official Guide 12th edition is misprinted, yes? In my book on p315 it says P1(1+ T1/0)? I believe the equation should be P1(1+ T1/100).

Yes, the equation should be P1(1+ T1/100)

Cheers,
Brent