d
While rounding off measurements, we use the following rules by convention:
1. If the digit to be dropped is less than $5,$ then the preceding digit is left unchanged.
2. If the digit to be dropped is more than 5 , then the preceding digit is raised by one.
3. If the digit to be dropped is 5 followed by digits other than zero, then the preceding digit is raised by one.
4. If digit to be dropped is 5 or 5 followed by zeros, then preceding digit is left unchanged, if it is even.
5. If digit to be dropped is 5 or 5 followed by zeros, then the preceding digit is raised by one, if it is odd Units and Measurements
Let us round off 2.745 to 3 significant figures. Here the digit to be dropped is $5,$ then preceding digit is left unchanged, if it is even. Hence on rounding off 2.745 , it would be 2.74
Now consider $2.737,$ here also the digit to be dropped is $5,$ then the preceding digit is raised by one, if it is odd. Hence on rounding off 2.735 to 3 significant figures, it would be 2.74