Answer:
2 3/4
Explanation:
To convert a percentage to a number in standard form, divide by 100%.
275%/100% = 2 75/100 = 2 3/4
The weight at 4 months is 2 3/4 times as heavy as the weight at 2 months.
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Comment on the wording of the question
The wording "times heavier" tends toward ambiguity, IMO. We use "heavier" when we're adding an amount: "4 pounds heavier" means 4 pounds is added to the original weight.
As we see above, 275% of the weight at 2 months is 2 3/4 times that weight. That is, the weight at 4 months is heavier than the weight at 2 months by 1 3/4 times the weight at 2 months. When we ask, "how many times heavier?", we could be asking for that difference (1 3/4 times heavier), rather than the multiplier of the weight (2 3/4 times as heavy).
This is why I prefer to use the wording "times as heavy" if the desired answer is the multiplier of weight.
Most folks don't pay too much attention to the subtleties of the meaning of the wording, so "times heavier" is usually interpreted to mean "times as heavy."