How many inches are in 3.5 feet? Step by Step

Step by step

The question

Question: change 3.5 feet into inches.

3.5 ft = ? in

There are four choices.

First we solve it, the normal way.

Then we pick.

1 Find the link

1 foot is 12 inches.

1 ft = 12 in

2 Make the unit fraction

We want inches, so inches go on top.

We have feet, so feet go at the bottom.

Top and bottom are the same amount.

So the fraction is 1, and times 1 keeps the size.

12 in1 ft = 1

Careful!

Not upside down.

Then the feet would not cross out.

Careful: not 3.5 ft × 1 ft12 in ✗

3 Multiply

We multiply 3.5 feet by the fraction.

3.5 ft = 3.5 ft × 12 in1 ft

Feet on top and at the bottom cancel, like numbers.

Cross them out.

Inches are left.

What is left: 3.5 times 12.

= 3.5 × 12 in

3.5 times 12 is 42.

So 3.5 feet is 42 inches.

= 42 in

4 Check

Does it make sense?

Inches are smaller than feet.

So we need more of them.

42 is more than 3.5.

Yes.

in smaller than ft → more: 42 > 3.5

And back the other way: 42 divided by 12 = 3.5.

We get 3.5 feet again.

So the answer is right!

back: 42 ÷ 12 = 3.5

5 Pick the choice

Our answer is 3.5 ft = 42 in.

That is choice D.

D) 42

6 Why not the others

A is 10.5.

Wrong: 3.5 × 3: that is yards to feet; a foot has 12 inches.

A) 10.5 ✗ 3.5 × 3: that is yards to feet; a foot has 12 inches

B is 15.5.

Wrong: added 12 instead of multiplying.

B) 15.5 ✗ added 12 instead of multiplying

C is 35.

Wrong: moved the decimal point: a foot has 12 inches, not 10.

C) 35 ✗ moved the decimal point: a foot has 12 inches, not 10

Let's look back.

First: find the link.

Then: make the unit fraction.

Then: multiply.

Then: check.

Then: pick the choice.

Last: why not the others.

Answer