Upper and Lower Bounds

Question 1:

When x = 20 (1 s.f.) and
y = 22 (2 s.f.), find the lower bound of x + y

36.5

Question 2:

When x = 33.96 (2 d.p.) and
y = 0.81 (2 d.p.), find the upper bound of x - y

33.16

Question 3:

When x = 7020 (3 s.f.) and
y = 405 (3 s.f.), find the upper bound of x × y

2848637.5

Question 4:

When x = 1200 (2 s.f.) and
y = 390 (2 s.f.), find the lower bound of x ÷ y

2.9113924050633