Guide 2 Chapter 2 Problems Set # 10

[nickiss20002000]

I do not understand how to use different benchmarks values to estimate fractions. 1/2 is the only fraction I am comfortable using as a benchmark value. I used it for this problem and ended up with :
9/17 slightly more than 1/2
3/16 lower than 1/2
19/20 more than 1/2
7/15 lower than 1/2
Then, I had to compare the more than 1/2 ones to see which one is bigger. I ended up spending 2.28 s on this question.
I read the solution, but I am confused about how how to come up with the solutions estimations to shorten my time on this problem.
Thanks

[tommywallach]

Hey Nic,

To do well on the GRE, you should know your decimal equivalents for ALL fractions that follow:

1/2 1/3 1/4 1/5 1/6 1/7 1/8 1/9 1/10
2/3 2/4 2/5 2/6 2/7 2/8 2/9 2/10
3/4 3/5 3/6 3/7 3/8 3/9 3/10
etc. etc. etc. etc. etc. etc. etc.

If you memorize all of these in their decimal forms, you will be able to benchmark effectively. (You have to ballpark 7ths (i.e. 1/7 = about .14, 2/7 = about .28, etc.) , but the rest of them are rational numbers.)

-t