Coaching Centre
Adding and subtracting negative integers
Adding and subtracting negative integers using the number line and the rules a + (−b) = a − b and a − (−b) = a + b.
The rules
Set b negative and compare a − b with a + b.
Evaluate $-12 - (-5) + (-8)$.
$-12 + 5 - 8$
$= -7 - 8 = -15$
A submarine at $-140$ m rises $65$ m, then dives $90$ m. Find its final depth.
$-140 + 65 - 90 = -75 - 90 = -165$
It is at $-165$ m (165 m below sea level).
$a - (-b)$
$a + b$
$-5 - 6$
$-11$
$-5 - (-6)$
$1$
Evaluate $-4 - (-9)$.
$-4 + 9$.
Evaluate $6 + (-11)$.
$6 - 11$.
Evaluate $-12 - (-5) + (-8)$.
$-12 + 5 - 8$.
A submarine at $-140$ m rises $65$ m then dives $90$ m. Find its depth.
$-140 + 65 - 90$.
Evaluate $-3 - 7$.
Both move left.
The temperature changes from $-8^\circ$C to $15^\circ$C. Find the change.
$15 - (-8)$.
Evaluate $-7 + 3 - (-4)$.
$-7 + 3 + 4$.
Evaluate $2 - 5 - (+3)$.
$2 - 5 - 3$.
New numbers every time. Keep going until you get five in a row.