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The number 9438 has 4 significant digits. When dropping the 8, the number 1 is added to the last retained digit, namely 3. Why? Because when the last digit is bigger than 5. We now have rounded 9438 to 3 significant digits: namely, 944.
The next number to be dropped if 4. It is less than 5, so there is no change to the preceding digit: namely, 4. So, rounding 944 to 2 significant digits yields 94.
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