Practice Exam #3 Question #18

[sanjit.shankar]

Question:
3.1n5
Let n represent the hundredths digit in the number shown above. If the number is rounded to the nearest tenth, which of the following could be the tenths digit in the rounded number

Options are: a.0 b.2 c.4 d.5 e.6
Correct answer is choice b, 2.

Given Explanation:
Rounding 3.1n5 to the nearest hundredth requires that we first consider the digit in the thousandths place, a 5. This means that we must round the n in the hundredths place up to n+1. For most values of n, the tenths digit would be unaffected by the rounding.
The number 3.1n5 presently has a 1 in the tenths place and if n is anything but 9, the tenths place will remain a 1 even after the rounding. However, 1 is not an answer choice.
If n were 9, rounding to the nearest hundredth would require rounding up both the hundredths and the tenths digits to 3.20 or 3.2. The number 2 could therefore be in the tenths place of the rounded figure.


But the explanation is wrong, it should be if n were 5 or higher instead of n being only 9 for the number 3.1n5 to be rounded up to 3.2. Not only is the given explanation wrong but there was a simpler explanation. The information regarding hundredths digit represented as n serves only to distract the test taker and I fell for it. The question asks what might be tenths digit. When we round the number 3.1n5, there are only two possibilities either 3.1 or 3.2 and since 1 is not among the given answer choices the correct answer is 2.

[tommywallach]

You're correct. When we round, we only look at the next digit over. So rounding to the nearest tenth ONLY requires us to know what the hundredth place is. The thousandth here is totally irrelevant as far as I can see.

-t