A rectangular metal plate is measured to be 7.6cm long and 3.1cm wide, both correct to one decimal place. What is the upper bound for its length?
Find the upper bound of its area. [write down all the numbers on your calculator display]

We know that the rectangular plate has measures of:

length = 7.6 ± 0.05 cm

width = 3.1 ± 0.05 cm

(the error is 0.05cm because we know that both measures are correct to one decimal place)

First, the upper bound of the length is equal to the measure of the length plus the error, this is:

L = 7.6 cm + 0.05 cm = 7.65 cm

The upper bound of the area is the area calculated when we use the upper bound of the length and the upper bound of the widht.

Remember that the area for a rectangle of length L and width W, is:

A = W*L

Then the upper bound of the area is:

A = (7.6cm + 0.05cm)*(3.1cm + 0.05cm) = 10.8 cm^2