Q1.
Complete these expressions. You may think of them as finding the movement needed to reach the Target Floor from the Starting Floor. a. (+ 1) – (+ 4) b. (0) – (+ 2) c. (+ 4) – (+ 1) d. (0) – (– 2) e. (+ 4) – (– 3) f. (– 4) – (– 3) g. (– 1) – (+ 2) h. (– 2) – (– 2) i. (– 1) – (+ 1) j. (+ 3) – (– 3)
Answer
Remember: Target Floor – Starting Floor = Movement needed. The first number is where you want to go, the second is where you are.
| Expression | From … to … | Movement | |
|---|---|---|---|
| a. | (+ 1) – (+ 4) | from Floor + 4 to Floor + 1 → 3 floors down | – 3 |
| b. | (0) – (+ 2) | from + 2 to 0 → 2 floors down | – 2 |
| c. | (+ 4) – (+ 1) | from + 1 to + 4 → 3 floors up | + 3 |
| d. | (0) – (– 2) | from – 2 to 0 → 2 floors up | + 2 |
| e. | (+ 4) – (– 3) | from – 3 to + 4 → 3 floors up to 0, then 4 more | + 7 |
| f. | (– 4) – (– 3) | from – 3 to – 4 → 1 floor down | – 1 |
| g. | (– 1) – (+ 2) | from + 2 to – 1 → 2 floors down to 0, then 1 more | – 3 |
| h. | (– 2) – (– 2) | from – 2 to – 2 → you are already there | 0 |
| i. | (– 1) – (+ 1) | from + 1 to – 1 → 2 floors down | – 2 |
| j. | (+ 3) – (– 3) | from – 3 to + 3 → 3 floors up to 0, then 3 more | + 6 |
Look at e, d and j: every time a negative number is subtracted the answer grows. (+ 4) – (– 3) = + 7 is the same as (+ 4) + (+ 3). Subtracting a negative number is the same as adding the matching positive number — you will meet this rule again on page 252.