Answer:
17/25
Explanation:
You want to know which of 5/16 or 17/25 is closer to 1/2.
Comparison
For the sake of argument, let's assume that 17/25 is closer to 1/2. This means the difference from 1/2 is smaller than for 5/16:
(17/25 -1/2) < (1/2 -5/16)
We can add (5/16 + 1/2) to both sides and we get ...
17/25 + 5/16 < 1
The sum on the left is easily computed:
(17·16 +25·5)/(25·16) < 1
(272 +125)/400 < 1
397/400 < 1 . . . . . . true
Our original premise is true: 17/25 is closer to 1/2.
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Additional comment
A straightforward solution involves finding the positive difference of each number from 1/2, then comparing those differences. The attached calculator screen does that. It shows the difference of 17/25 from 1/2 is smaller than for 5/16, in agreement with the above.
Effectively, we're comparing the midpoint between the two numbers to 1/2. If it is below 1/2 (which it is), then the upper number doesn't have as great a distance from 1/2 as the lower number does.
This sort of comparison only works if the numbers are on either side of 1/2. If they are on the same side, the sign of their difference tells the tale.