Memorizing FractionsWhich Fractions? and to Which Decimal Place?

Question

I'm planning to make my own flashcards for fraction values converted to irrational numbers. To which decimal place should I go to for non-repeating fractions?

I've been searching for this information, because people seem to know exactly what decimal amount to convert a fraction to and they make use of that. For example, instantly recognizing 7/8 is 0.875 and using this to their advantage to solve the problem. Still, I haven't found good information on which fractions I should memorize even though my test prep service (TTP) is telling me it's useful to memorize them.

I just figured I would memorize values with denominators of 2-12, all the way up to 11/12 (so for 5 I would memorize 1/5, 2/5, 3/5, 4/5).

Not sure if this is excessive, however.

Archit3110 · Answer

Only basic fractions value are to be remembered.. 1/5 to 4/5 .. rest can be calcuated according to question

MyGMATbuddy · Answer

You don’t need to memorize too many—just the most common fractions that show up repeatedly in PS and DI questions. Here’s what I recommend:

Must-know (with decimals up to 2–3 places):

* 1/2 = 0.5
* 1/3 ≈ 0.333
* 2/3 ≈ 0.667
* 1/4 = 0.25
* 3/4 = 0.75
* 1/5 = 0.2
* 2/5 = 0.4
* 3/5 = 0.6
* 4/5 = 0.8
* 1/6 ≈ 0.167
* 5/6 ≈ 0.833
* 1/8 = 0.125
* 3/8 = 0.375
* 5/8 = 0.625
* 7/8 = 0.875
* 1/9 ≈ 0.111
* 2/9 ≈ 0.222, and so on
* 1/10 = 0.1

These pop up in percentages, rate problems, and IR/DI graphs. Once these are second nature, it’ll save time and reduce silly mistakes.

Pankaj Jindal | GMAT Classic 730 | IIM Bangalore | Helping working professionals
Success story: https://gmatclub.com/forum/how-i-scored ... l#p3588949

WhitEngagePrep · Answer

I would say that up to 12 is excessive! You only really need to memorize what I've highlighted in yellow, as the rest can be found quickly with a pattern! Memorize /2, /3, and /4 (both under and over 1) 1/2 =0.5 1/3 =0.333 1/4 =0.25 3/2 =1.5 2/3 =0.667 2/4 =0.5 4/3 =1.333 3/4 =0.75 5/4 =1.25 Notice the pattern for /9 and /10 1/9 =0.111 1/10 =0.1 2/9 =0.222 2/10 =0.2 3/9 =0.333 3/10 =0.3 ... ... 9s are the numerator repeating 10s are moving the decimal place 1 You can use conversion for the /5s and most of the /6s and /8s /5 can be quickly converted to /10 by doubling both, so no need to memorize... 1/5=2/10 2/5=4/10 3/5=6/10 ... Most of the /6s and /8s can be reduced to /3s or /4s first. And I've only ever seen you need 1/6, 1/8 and 3/8 so memorize those (and ignore the rest) 1/6 =0.167 1/8 =0.125 2/6=1/3 2/8=1/4 3/6=1/2 3/8 =0.375 4/6=2/3 4/8=1/2 5/6=ignore 5/8=ignore 6/8=3/4 7/8=ignore And then completely ignore the /7, /11, or any /12 that can't be reduced to something nicer (In 20 years I've never needed to know 1/12, 5/12, 7/12, or 11/12) Hope this helps!

Whit

1/2=0.5	1/3=0.333	1/4=0.25
3/2=1.5	2/3=0.667	2/4=0.5
	4/3=1.333	3/4=0.75
		5/4=1.25

1/9=0.111	1/10=0.1
2/9=0.222	2/10=0.2
3/9=0.333	3/10=0.3
...	...

Memorizing FractionsWhich Fractions? and to Which Decimal Place?

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1/6=0.167	1/8=0.125
2/6=1/3	2/8=1/4
3/6=1/2	3/8=0.375
4/6=2/3	4/8=1/2
5/6=ignore	5/8=ignore
	6/8=3/4
	7/8=ignore

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Memorizing FractionsWhich Fractions? and to Which Decimal Place?

Prep Toolkit

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My Rewards