Upper and Lower Bounds

Question 1:

When x = 660 (2 s.f.) and
y = 4320 (3 s.f.), find the upper bound of x + y

4990

Question 2:

When x = 9860 (3 s.f.) and
y = 72.9 (3 s.f.), find the lower bound of x - y

9782.05

Question 3:

When x = 100 (1 s.f.) and
y = 3900 (2 s.f.), find the lower bound of x × y

365750

Question 4:

When x = 6.243 (3 d.p.) and
y = 0.7 (1 d.p.), find the upper bound of x ÷ y

9.6053846153846