Quick Math Trick with Fractions

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Lunasly

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Hello everyone,

I am looking for a quick math trick of estimating fractions as decimals. For example: What would you do to estimate 31.5/58.6? I know it's close to 1/2, but...

I have two answer choices I need to pick between:

A) 0.504
B) 0.539

Answer is B.

Thanks,
Lunasly.

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Hello everyone,

I am looking for a quick math trick of estimating fractions as decimals. For example: What would you do to estimate 31.5/58.6? I know it's close to 1/2, but...

I have two answer choices I need to pick between:

A) 0.504
B) 0.539

Answer is B.

Thanks,
Lunasly.

I don't any trick per se, but if I were looking at this and saw A) I'd say that is pretty much 0.5. Looking at 58.6, half of that should be 29.3. 31.5 is well above 29.3 so it'd have to be B). If you're not satisfied with that you could ask what is 0.51 of 58.6? Well, 29.3 is 0.5 of 58.6 and 0.58 is 0.01 of 58.6, so 0.51 of 58.6 would be 29.3+0.58=29.88. 0.504<0.51<0.539 and since we know that 0.51*58.6=29.9 and 31.5>29.9 we can eliminate A) and accept B).
 
Looking at the answer choices, my first thought was the same as red october's; choice A is essentially equivalent to exactly one half, and choice B is slightly above one half. Without even doing any math, I look at 31.5 and say no, that's not exactly one half of 58.6, and since the actual half should be less, then 31.5 is slightly more than one half, so the answer is B.
 
I don't think I had to use long division on my actual MCAT, but it's an easy and useful skill to know.
 
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Hello everyone,

I am looking for a quick math trick of estimating fractions as decimals. For example: What would you do to estimate 31.5/58.6? I know it's close to 1/2, but...

I have two answer choices I need to pick between:

A) 0.504
B) 0.539

Answer is B.

Thanks,
Lunasly.

There is no trick. Theres no way that 31.5/58.6 could be .504. Think about it.
 
Maybe one way:

31.5/58.6

15.5/29.3

8/15

4/7.5

2/3.75

1/1.8 ---> greater than 1/2 or about 1.55
 
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