Percent of a quantity; finding the percent and the whole

About this lesson

Grade 7 › Percentages

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Percent of a quantity; finding the percent and the whole

Warm-up

Three quick questions from earlier lessons.

Discover

A class of 40 students: 25% walk to school. How many walk?

10
25

Key idea

Percent means per hundred.

p\%

of a whole is

\tfrac{p}{100} \times \text{whole}

. What percent? part ÷ whole × 100. Find the whole: part ÷

\tfrac{p}{100}

.

Worked example

30% of a number is 12.

\text{whole} = 12 \div 0.3

0.3 × whole = 12.

40

Divide.

Your turn, guided

Your turn: what percent of 80 is 20?

25

20 ÷ 80 × 100.

Practice ★

What is 50% of 340?
What is 5% of 300?

What percent of 140 is 7?

Watch out!

Practice ★★

60% of a number is 228. What is the number?
45% of a number is 162. What is the number?

Exit ticket

Three questions to check you have got it.

What is 50% of 340?
What is 5% of 300?
What is 40% of 400?

Summary card

Percent of a quantity

$p\% = p/100$ ; percent = part ÷ whole × 100.

Watch out: divide the part by the whole, not the reverse.

End of the lesson

Next lesson: Percent increase and decrease: tax, tips, discounts Back to the chapter

Answers: Percent of a quantity; finding the percent and the whole

A

$170$
$15$

B

$5$

C

$380$
$360$

D

$170$
$15$
$160$

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