Percent Mental Math

Welcome to Intro to

Percent Workshop!

What are some examples of percent you see around you?

Learning Outcomes

At the end of the workshop, you will be able to...

• Understand the concept of percent and its relationship to fractions and decimals

• Convert between fractions, decimals and percentages

• Solve simple percentage calculations (of, is and what percent)

• Employ mental math techniques and shortcuts for quick and accurate percentage calculations

So what is a "per cent"?

A percent is a ________ expressed in hundredths!

​How can 75% be expressed as a ratio? Can this be expressed in any other way?

​A percent is based on a hundred and represents a portion of a whole.

​

Converting between

Fractions, Decimals, and Percentages

Multiple Choice

How do you express 11% as a fraction?

• $$\frac{11}{10}$$

• $$\frac{11}{100}$$

• $$\frac{100}{11}$$

• $$\frac{11}{1000}\text{}$$

Multiple Choice

How do you express 11% as a decimal?

• 0.11

• 1.1

• 0.011

• 11

Multiple Select

Choose the correct decimal and fraction form of 8%.

• $$\frac{4}{5}$$

• $$\frac{2}{25}$$

• $$\frac{2}{50}$$

• 0.08

• 0.8

Percent → Fraction/Decimal

___________ by ______

Move the decimal place _____ to the left

Decimal

Fraction*

*Ensure that the fraction answer is reduced when needed!

Multiple Choice

Express 0.3% as a decimal form.

• 0.3

• 0.03

• 0.003

• 0.0003

Multiple Choice

Express 0.3% as a fraction form.

• $$\frac{0.3}{100}$$

• $$\frac{3}{10}$$

• $$\frac{3}{100}$$

• $$\frac{3}{1000}$$

Multiple Select

Express $$\frac{1}{4}\%$$ as a decimal and fraction form.

• $$\frac{1}{400}$$

• $$\frac{1}{4}$$

• $$\frac{100}{4}$$

• 0.25

• 0.0025

Fraction/Decimal → Percent

___________ by ______

Move the decimal place _____ to the _________

Decimal:

​Practice

Solving Simple Percentage Calculations

​Example: What is 18% of 300?

​Example: 54 is 18% of what number?

​Example: 54 is what percent of 300?

Multiple Choice

What is 7% of 52? Choose the correct expression.

• 52 ÷ 0.07

• 52 × 7

• 52 × 0.7

• 52 × 0.07

Multiple Choice

14% of what number is 80? Choose the correct expression.

• 80 × 1.4

• 80 × 0.14

• 80 ÷ 0.14

• 80 ÷ 14

Multiple Choice

93 is what percent of 9? Choose the correct expression.

• $$\frac{93}{9}$$

• $$\frac{93}{9}\times100$$

• $$\frac{9}{93}\times100$$

• 93 × 9

​The Triangle Method

​The percentage problems always involve three values:

1.

2.

3.

​

​Ex 1) 15 out of 50 is 30%

Ex 2) What is 31% of 140

Ex 3) 24% of what number is 80?

Percent Change

To find the percent change, what do you think you need to find first?

When two numbers that are being compared involve a change
whether it's an increase or decrease.

Example: The production of masks dropped 10% from last year.

The price of gas rose 5% over the last two years.

Percent Change

Formula:

​Remember: The change is compared or divided by the original value then multiplied by 100 to make it a percentage!

​Example: The price of a same pencil rose from $1.25 to $2.05. What is the percent change in the price of the pencil?

Any questions or feedback?

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Thank you!