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 From B. Lee Clay

Squaring Numbers

Multiplying Numbers

Dividing Numbers

Subtracting Numbers

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Multiplying a 2-digit number by 4.7

1. Select a 2-digit number.
2. Multiply the number by seven.
3. Move the decimal point one place to the left.
4. To this add four times the original number.

Example:

1. The 2-digit number chosen to multiply by 4.7 is 21.
2. Multiply by 7: 7 × 21 = 147.
3. Move decimal point one place left: 14.7.
4. Add this to four times the original number: 14.7 + 4(21) = 14.7 + 84 = 94 + 4.7 = 98.7.
5. So 4.7 × 21 = 98.7.

See the pattern?

1. The 2-digit number chosen to multiply by 4.7 is 62.
2. Multiply by 7: 7 × 62 = 420 + 14 = 434.
3. Move decimal point one place left: 43.4.
4. To this add two times the original number: 43.4 + 4(62) = 43.4 + 240 + 8 = 51.4 + 240 = 291.4.
5. So 4.7 × 62 = 291.4.

Keep on adding and multiplying left to right and these answers will come quickly and accurately.