Hi all,

Just wondering what is your guys reasonning to QUICKLY solve a percentage such as 15% of 35, 50 $

I am refering as example as a question like 139,

OG 12th Edition, Problem Solving:

A meal cost $ 35.50 adn there was no tax. If the tip was more than 10 pc but less than 15pc of the price, then the total amount paid should be:

A. 40-42

B. 39-41

C. 38-40

D. 37-39

E. 36-37

Fin here under my reasonning, I would appreciate your comments.

10 pc of 35.50= kidstuff! = 35, 50 + (35,50/10)= 39, 05

mmmm let's have a look at the answer choices, B seems to be correct at 80% sure (only answer including 30 as the least value), would be nice if I could confirm it by finding the other value.

15 pc of 35.50 believe it or not, it takes me about 1 min to find out that it is about 40,8... I would appreciate to know how you guys make such a percentage quickly?

Even by making 1,15* 35,50 it takes time to calculate it toroughly.

- Those is the 138 th question out of the 230 PS in the OG, what's the level of such and the questions before sub 600? At what question does it starts to be above 600 ? Not really fair from GMAC to provide just 1/4 or 1/3 of 600+ questions

- I am looking for a great ressource to review some theory about inequation and absolute value, free if possible..?