12 of 40 students walk to school. About how many of 600 walk? Easy

The question

Question: 12 of 40 students walk to school.

About how many of 600 walk?

1 The fraction in the sample

12 out of 40: that is 12/40.

The 40 students are a sample: a small group that stands for everyone.

12 and 40 can both be divided by 4.

So it is 3/10.

2 Use it for everyone

We expect the same fraction of all 600: 3/10 of 600.

Of means times.

600 divided by 10 is 60.

Then times 3.

That is about 180.

Careful!

A sample only shows about how many.

So the answer is a good guess, not an exact count.

So about 180 students walk.

3 Check

Let's check: 180 out of 600.

Divide the top and the bottom by 60: 3/10, the same fraction as the sample.

So the answer is right!

Let's look back.

First: the fraction in the sample.

Then: use it for everyone.

Last: check.

▶ Watch it solved

In a sample of 50 bulbs, 2 were broken. About how many of 1,000 are… Medium

The question

Question: In a sample of 50 bulbs, 2 were broken.

About how many of 1,000 are broken?

1 The fraction in the sample

2 out of 50: that is 2/50.

The 50 bulbs are a sample: a small group that stands for everyone.

2 and 50 can both be divided by 2.

So it is 1/25.

2 Use it for everyone

We expect the same fraction of all 1,000: 1/25 of 1,000.

Of means times.

1,000 divided by 25 is 40.

That is about 40.

Careful!

A sample only shows about how many.

So the answer is a good guess, not an exact count.

So about 40 bulbs are broken.

3 Check

Let's check: 40 out of 1,000.

Divide the top and the bottom by 40: 1/25, the same fraction as the sample.

So the answer is right!

Let's look back.

First: the fraction in the sample.

Then: use it for everyone.

Last: check.

▶ Watch it solved

In a sample of 120 phones, 9 were faulty. About how many of 2,400… Harder

The question

Question: In a sample of 120 phones, 9 were faulty.

About how many of 2,400 are faulty?

1 The fraction in the sample

9 out of 120: that is 9/120.

The 120 phones are a sample: a small group that stands for everyone.

9 and 120 can both be divided by 3.

So it is 3/40.

2 Use it for everyone

We expect the same fraction of all 2,400: 3/40 of 2,400.

Of means times.

2,400 divided by 40 is 60.

Then times 3.

That is about 180.

Careful!

A sample only shows about how many.

So the answer is a good guess, not an exact count.

So about 180 phones are faulty.

3 Check

Let's check: 180 out of 2,400.

Divide the top and the bottom by 60: 3/40, the same fraction as the sample.

So the answer is right!

Let's look back.

First: the fraction in the sample.

Then: use it for everyone.

Last: check.

▶ Watch it solved