Q1.
Try evaluating the following expressions by similarly drawing or imagining a suitable lift: a. – 125 + (– 30) b. + 105 – (– 55) c. + 105 + (+ 55) d. + 80 – (– 150) e. + 80 + (+ 150) f. – 99 – (– 200) g. – 99 + (+ 200) h. + 1500 – (– 1500)
Answer
Imagine an ‘infinite lift’ with Level 0 in the middle. Read each expression as a journey.
| Expression | Journey in the imaginary lift | Answer | |
|---|---|---|---|
| a. | – 125 + (– 30) | Start at – 125 and go 30 more levels down | – 155 |
| b. | + 105 – (– 55) | From – 55 to + 105: 55 up to 0, then 105 more up | + 160 |
| c. | + 105 + (+ 55) | Start at + 105 and go 55 levels up | + 160 |
| d. | + 80 – (– 150) | From – 150 to + 80: 150 up to 0, then 80 more up | + 230 |
| e. | + 80 + (+ 150) | Start at + 80 and go 150 levels up | + 230 |
| f. | – 99 – (– 200) | From – 200 to – 99: 101 levels up | + 101 |
| g. | – 99 + (+ 200) | Start at – 99, go 200 up: 99 to reach 0, 101 above it | + 101 |
| h. | + 1500 – (– 1500) | From – 1500 to + 1500: 1500 up to 0, then 1500 more | + 3000 |
The pattern to spot: b and c give the same answer, d and e give the same answer, f and g give the same answer. In each pair the first one subtracts a negative and the second one adds the matching positive. So – (– n) = + n.