og ps 123

Enginpasa1 wrote:I believe I am making this much harder than it really is. please let me know.

The price of lunch for 15 peoplewas $207.00including a 15% gratuity for service. What was the average price per person, Excluding gratuity?

a.11.73
b.12.00
c.13.80
d.14.00
e.15.87

qa iis B i chose A

I would simply plug-in the results and see what fits. The most attractive option to start with is B , because 12 is an easy to number to do calc with.

If the average price per person is 12, then 15 people paid 15 X 12 = 180 for their lunch, without gratuity. gratuity is 15%, or 180 X 15 / 100 = 27. 180 + 27 = 207 which was the total price they paid, so answer B.

Hey there,
If you got [A], then must be doing it this way [0.85*207] / 15 = 11.73. But, it should be done in a slightly different way
==> [207 / 1.15] / 15 = 180 / 15 = 12

Hope this helps!

i often forget to combine the two percents in that manner.. I also keep forgetting of a great tool of backsolving. thanks folks[spoiler][/spoiler]

Common mistake is calculating tip as 15% of total bill (207 in this case)...

It should be, Original amount (x) + 15% of x = 207.

thanks for pointing this out Vaghul.. but I didn't understand why it's wrong if I assume that the total amount is 207 and then: 207- 15/100 (207) I would come up with original amount?

X(Lunch Price) + 15%X = 207
X( 1 + 3/20) = 207
23X/20=207
X= 180
Average = 180(Lunch price)/15(Number of people)
Average = 12

The key here is realizing that 15% is 3/20...and that 207/23 is 9..(This question shouldn't take you more the 40 secs if you recognize these two steps)

I don't like the testing numbers strategy because if you aren't lucky, you will waste time.

IF YOU HAVE TO MULTIPLY OR DIVIDE A PERCENT/DECIMAL, CONSIDER FRACTIONS!!

yea, good point...you can get stuck in endless calculations which might take forever in GMAT to calculate 207/1.15.

I realized this and then used second method - substituting the answers and luckily 12 (first easy number) worked out perfectly.

But, I agree, fractions work better / quicker in this case.