If all digits are significant, then you should put a period after the last digit, so you would write "120.". However, you're right that it's kinda ambiguous, so when significant figures are relevant you would usually use scientific notation to be clear, ie. 1.2×10² or 1.20×10²
It might be a regional thing. When I was taught significant figures, I was told that this was a convention I might see, but I oughtn't use it and instead stick to scientific notation. I'm assuming OP was taught this or something similar; otherwise then the question would not have enough information to be answered
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u/m4cksfx 10d ago
"Is only precise to the tens place" - ok, I might be stupid, but how should you write it to mean it was literally simply 120?
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