Answer:
2.5
Explanation:
When the number is rounded to two significant figures, the left-most digit will be non-zero, and there will be one more significant digit to the right of it.
Here, we need to round the number to 2 significant figures. Find the third digit from the left. If it is 5 or more (it is), then increase the second digit from the left before removing all digits to the right of it.
2.456 rounds to 2.5
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Additional comment
Leading zeros are never significant. Trailing zeros are only significant if the number has a decimal point. Any digits between leading and trailing zeros are significant. All mantissa digits of a number in scientific notation are significant.
When rounding to a specific number of significant digits, as here, the significant digits are counted from the left.