Modelling Integer Changes

≈ 35 min

Modelling Integer Changes

A word problem with integers becomes easier when you make a small table: starting value, each change, final value. A rise, deposit or move right is positive; a drop, debt or move left is negative. Write the story as one number sentence before calculating, then decide whether the final answer makes sense in the context.

Worked example

A hiker starts at $-3$ m relative to a reference point, climbs 12 m and then descends 5 m. $-3+12-5=4$ , so the hiker finishes 4 m above the reference point.

Exam method

Mark each change as positive or negative. 2. Write one expression. 3. Calculate in order and attach the context and unit.

A temperature starts at $-4^\circ\text{C}$ , rises $9^\circ\text{C}$ and then falls $6^\circ\text{C}$ . What is the final temperature?

Which expression models a R30 debt followed by a R50 deposit?

$-30+50$

$30-50$

$-30-50$

$30+50$

A diver is at $-8$ m, rises 15 m, then descends 4 m. What is the final position in metres?

Write the sign ( $+$ or $-$ ) for a withdrawal from a bank account.