AI Tutor
Imagine waking up on a freezing winter morning where it is −4∘extC-4^\circ ext{C}, but by lunchtime the sun comes out and warms the air to 6∘extC6^\circ ext{C}.
How many total degrees did the temperature actually rise?
To find out, we have to follow the temperature as it climbs straight through zero.

Warming Up Through Zero

A vertical thermometer works just like an upright number line, with 0∘0^\circ standing right in the middle.
When temperature climbs from below zero to above zero, break the journey into two separate jumps: first to zero, then past zero.
The climb from −4∘-4^\circ up to 0∘0^\circ is 4∘4^\circ, and the climb from 0∘0^\circ up to 6∘6^\circ is 6∘6^\circ.
Adding both parts together gives a total rise of 4+6=10∘extC4 + 6 = \mathbf{10^\circ ext{C}}.
What happens when the sun goes down and the temperature heads in the opposite direction?

Cooling Down Through Zero

A temperature fall works the exact same way, but the jumps move downward.
Suppose a cozy afternoon starts at 5∘extC5^\circ ext{C} and drops overnight into a frost at −3∘extC-3^\circ ext{C}.