When we round 742396 to four significant digits, then we get the answer of 742400
What we do is circle the first four digits on the left which are the 7,4,2, and 3. That last 3 will bump up to a 4 because we round up to the nearest hundred (due to the next digit being a 9, which is greater than 5).
Put another way, 742396 is closer to 742400 than it is to 742300. The zeros in 742400 are not significant.
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When we round 742396 to two significant digits, then we get the answer 740000
This time, we only keep the 7 and the 4 as our two important digits. Everything else becomes a 0 which isn't significant. No rounding happens since the 2 after the 4 isn't larger than five. I.e. the number 742396 is closer to 740000 than it is to 750000
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Rounding 0.07284 to three significant digits gets us to the answer 0.0728
We drop the 4 at the end because the 7,2, and 8 take up the three digits we want to keep. The two zeros are not significant.
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Rounding 0.07284 to two significant digits gets us the answer 0.073
We keep the 7 and 2 as our two important digits, but bump that 2 up to a 3 because the next digit over is larger than five.
