THE TRANSITION LINE // FIELD NOTES // STOP 30
Percent change and root estimates
Field Book
Lessons 113 to 116
Method
Pencil and paper. Calculators never.
Markdowns at the depot store, and a root trapped between two perfect squares. Percent increase and decrease move an original amount by a portion of itself, equations sort into always true, always false, and conditional, imperfect roots get trapped between neighboring perfect squares, and weight units convert by multiplier.
What you have to be able to do
- Compute percent increase and decrease
- Classify equations as true, false, or conditional
- Estimate square roots between perfect squares
- Convert weight and mass units
The procedures
Percent increase and decreaseField Book Lesson 113
- Find the percent of the original amount.
- Add it for an increase, subtract it for a decrease.
Three kinds of equationsField Book Lesson 114
- Always true, always false, or conditional.
- A conditional is true only under its condition: name the condition.
Estimating rootsField Book Lesson 115
- Trap the number between two neighboring perfect squares.
- The root sits between their roots.
Weight conversionsField Book Lesson 116
- Build the unit multiplier from the weight facts: ounces, pounds, tons, grams, kilograms.
- Disappearing unit on the bottom.
Worked: the markdown
- 30% off 240: the portion is 0.30 ยท 240 = 72.
- 240 - 72 = 168
Worked: trap the root
- √58: since 49 is less than 58 and 58 is less than 64,
- √58 sits between 7 and 8.
Terms on the record
| Term | Meaning |
|---|
| percent increase | a portion of the original added onto the original |
| percent decrease | a portion of the original taken away from the original |
| conditional equation | an equation true only when its condition holds |