Upper and Lower Bounds

Question 1:

When x = 0.515 (3 d.p.) and
y = 4.51 (2 d.p.), find the lower bound of x + y

5.0195

Question 2:

When x = 8000 (1 s.f.) and
y = 1600 (2 s.f.), find the lower bound of x - y

5850

Question 3:

When x = 0.249 (3 d.p.) and
y = 3.34 (2 d.p.), find the upper bound of x × y

0.8345775

Question 4:

When x = 4.21 (2 d.p.) and
y = 0.58 (2 d.p.), find the lower bound of x ÷ y

7.1880341880342