Answer:
When rounding to 1 significant figure, we keep the first non-zero digit and drop all the remaining digits. In this case, the first non-zero digit is 2, so we keep that and drop all the remaining digits:
a) 276040 rounds to 3 x 10^5 (or 300000 in standard form).
So the rounded number to 1 significant figure is 3 x 10^5.