A rectangle is 12 cm long and 7.5 cm wide. What is its area, in…

Step by step

The question

Question: find the area of a rectangle 12 long and 7.5 wide.

There are four choices.

First we solve it, the normal way.

Then we pick.

1 What area means

Area is how much space is inside.

We count the 1 by 1 squares that fit.

The length is 12.

The width is 7.5.

2 Length times width

So the area is length times width: A = length × width.

Squares in a row, times the rows.

Now put the numbers in: length = 12 and width = 7.5.

Forget the points: 12 times 75 is 900.

7.5 is 75 tenths.

So the answer is 900 tenths.

That is 1 digit after the point: 90.0, which is 90.

So the area is 90 square units.

3 Pick the choice

Our answer is A = 90.

That is choice C.

4 Why not the others

A is 19.5.

Wrong: 12 + 7.5: added the sides.

B is 39.

Wrong: that is the perimeter.

D is 180.

Wrong: doubled it: the area is length × width.

Let's look back.

First: what area means.

Then: length times width.

Then: pick the choice.

Last: why not the others.