THE TRANSITION LINE // FIELD NOTES // STOP 10
Decimal add and subtract, and the negatives arrive
Field Book
Lessons 37 to 40
Method
Pencil and paper. Calculators never.
Below-zero freight checks in: depth, debt, and degrees. Decimal points line up before any column moves, whole numbers dress as decimals to join them, the harder percents reduce to fractions in three families, and negative numbers step onto the left half of the line.
What you have to be able to do
- Add and subtract decimal numbers
- Pad whole numbers with a decimal point and zeros
- Change percents over 100, decimal percents, and fractional percents to fractions
- Read real situations as negative numbers
The procedures
Adding and subtracting decimalsField Book Lesson 37
- Line up all the decimal points first.
- Then work the columns exactly as with whole numbers.
Wholes among decimalsField Book Lesson 38
- Write a whole number as itself point zero.
- Pad zeros until the places match, then work the columns.
Harder percents to fractionsField Book Lesson 39
- Over 100 percent: the fraction comes out improper.
- A decimal percent: expand by tens to clear the decimal, then reduce. A fractional percent: improper form times 1100.
Negative numbersField Book Lesson 40
- A negative is the opposite of its number, the same distance left of zero.
- Read drops as negatives: depth below surface, money owed, degrees below zero.
Worked: pad and subtract
- 40 - 3.65: write the whole number as 40.00.
- 40.00 - 3.65 = 36.35
Worked: a decimal percent
- 12.5% = 12.5100. Expand by ten: 1251000.
- Reduce: 18.
Terms on the record
| Term | Meaning |
|---|
| negative number | the opposite of a number, sitting left of zero |
| opposite | the number the same distance from zero on the other side |
| additive inverse | another name for the opposite of a number |