If a problem solving question asks you to answer to the nearest 0.1 percent, how exactly do you go about it?

I’m asking because while solving the Offical GRE quant practice set 2, I calculated the answer to be 15.73… and wrote the answer as 15.7. But, the solutions show the answer to be 15.8.

Have I done something wrong? Will this count as an incorrect answer?

15.73 must round to 15.7. I think you’ve made some sort of precision error - what’s the question?

Jack’s salary in 2011 = x

Arnie’s salary in 2011 = y

Jack’s salary in 2012: 1.1x

Arnie’s salary in 2012: 0.95y

We have

1.1x = 0.95y

y/x = 1.15789

The percentage difference is hence 15.789%, which rounds to 15.8%. Check your work again.

So, I actually chose numbers here:

I assumed the salary to be 100 for both Jack and Arnie.

And then in 2011, we have the salaries as Jack (x) and Arnie (y).

Thus, Jack’s Salary in 2012 — 1.1x=100

Which leads us to 90.9

And Arnie’s salary in 2012 —0.95y=100

Which leads us to 105.2631…

In this case, if we take only the first digit after the decimal for Arnie’s salary (i.e. 105.2), then we end up with 15.73 which is what I did.

If we take 2 digits after the decimal (i.e. 105.26), we end up with 15.79

Is there a rule of thumb to choose 2 digits or something?

The question here is about *precision*. GRE normally doesn’t set questions that force you to think about it, but when you’re asked to round to 0.1, I would certainly be careful to ensure accuracy.

For the record, when I took exact values with choosing numbers (i.e, your example), it rounded off to 15.8% as expect.

What do you mean by ‘exact values’?

Also, would the same requirement of precision be warranted even if the phrase nearest to 0.1 percent is not mentioned? If i have the answer with 5 digits after the decimal point, do I answer with all 5

And will we have any question where this phrase is not mentioned but the answer is a decimal value?

By that, I meant to 16 decimal places (as reported by my calculator).

Depends - you should not need to work with more than 3 or 4 decimal places. From a GregMAT+ perspective, we try not to set questions that require fiddling with precision that much for this reason, and ETS is unlikely to either.

If i have the answer with 5 digits after the decimal point, do I answer with all 5

The question should clarify how many decimal places to round to. Having to round to 5 is going to be very unlikely - it’s going to be very rare to set a question where the lack of precision specifically trips people. I usually encounter such problems in scientific computing, not a GRE question.

And will we have any question where this phrase is not mentioned but the answer is a decimal value?

Perhaps, but from a GregMAT+ perspective, this usually means that the answer terminates to one or two decimal places.