Upper and Lower Bounds

Question 1:

When x = 0.4 (1 d.p.) and
y = 0.28 (2 d.p.), find the lower bound of x + y

0.625

Question 2:

When x = 3240 (3 s.f.) and
y = 90 (1 s.f.), find the lower bound of x - y

3140

Question 3:

When x = 2.74 (2 d.p.) and
y = 0.328 (3 d.p.), find the lower bound of x × y

0.8957125

Question 4:

When x = 90 (1 s.f.) and
y = 21 (2 s.f.), find the upper bound of x ÷ y

4.6341463414634