Upper and Lower Bounds

Question 1:

When x = 830 (2 s.f.) and
y = 4000 (1 s.f.), find the lower bound of x + y

4325

Question 2:

When x = 6.57 (2 d.p.) and
y = 5.04 (2 d.p.), find the lower bound of x - y

1.52

Question 3:

When x = 6 (1 s.f.) and
y = 42 (3 s.f.), find the upper bound of x × y

273.325

Question 4:

When x = 5.317 (3 d.p.) and
y = 0.937 (3 d.p.), find the lower bound of x ÷ y

5.6709333333333