Strictly speaking, in Phys, you don't round off to significant figures until your final answer, because it might affect your answer. But yes, as a general rule, you do round off to the least number of SF. So 40 + 5.0 = 54. Similarly, 20.2*3 = 61.
Strictly speaking, in Phys, you don't round off to significant figures until your final answer, because it might affect your answer. But yes, as a general rule, you do round off to the least number of SF. So 40 + 5.0 = 54. Similarly, 20.2*3 = 61.