## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
Practice Exercises

Full List

### Multiplying a 2-digit number by 79 1/2

1. Select a 2-digit number.
2. Divide the number by 2.
3. Subtract this from 80 times original number.

#### Example:

1. The 2-digit number chosen to multiply by 79 1/2 is 21.
2. Divide by 2: 21/2 = 10 1/2.
3. Subtract this from 80 times original number: 80(21) - 10 1/2 = 1600 + 80 -10 1/2 = 1680 - 10 1/2 = 1670 - 1/2 = 1669 1/2.
4. So 79 1/2 × 21 is 1669 1/2.

See the pattern?

1. The 2-digit number chosen to multiply by 79 1/2 is 66.
2. Divide by 2: 66/2 = 33.
3. Subtract this from 80 times original number: 80(66) -33 = 4800 + 480 - 33 = 4800 + 450 - 3 = 5250 - 3 = 5247.
4. So 79 1/2 × 66 is 5247.
Multiply left to right in easy to handle increments and you will be able to give these products without a calculator.
The text provides a method for multiplying a 2-digit number by 79 1/2, including two examples that show the steps and the final answers.
multiple_questions_with_answers
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
## BEATCALC:  Beat the Calculator!

Back to Calculation Tips & Tricks

 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

Finding Percents

Calculation
Practice Exercises

Full List

### Multiplying a 2-digit number by 79 1/2

1. Select a 2-digit number.
2. Divide the number by 2.
3. Subtract this from 80 times original number.

#### Example:

1. The 2-digit number chosen to multiply by 79 1/2 is 21.
2. Divide by 2: 21/2 = 10 1/2.
3. Subtract this from 80 times original number: 80(21) - 10 1/2 = 1600 + 80 -10 1/2 = 1680 - 10 1/2 = 1670 - 1/2 = 1669 1/2.
4. So 79 1/2 × 21 is 1669 1/2.

See the pattern?

1. The 2-digit number chosen to multiply by 79 1/2 is 66.
2. Divide by 2: 66/2 = 33.
3. Subtract this from 80 times original number: 80(66) -33 = 4800 + 480 - 33 = 4800 + 450 - 3 = 5250 - 3 = 5247.
4. So 79 1/2 × 66 is 5247.
Multiply left to right in easy to handle increments and you will be able to give these products without a calculator.
user
The text provides a method for multiplying a 2-digit number by 79 1/2, including two examples that show the steps and the final answers.

TYPE: MULTIPLE_QUESTIONS_WITH_ANSWERS