Temperature: −3.5°F + (4 × 2.5°F)
At 6 a.m. it was negative three point five degrees. Each hour it warms up by two and a half degrees. What's the temperature four hours later?
Two operations hide in this story. First we'll multiply to find the total rise, then we'll add it to our starting temperature.
Step one: four hours, each rising two and a half degrees. That's four times two point five.
Four times two point five is ten. So the temperature rose ten degrees in all.
Step two: start at negative three point five, then add ten. Let's use a number line.
Here's where we begin — negative three point five, just left of zero.
Now we hop ten units to the right because the temperature went up by ten.
We land on positive six point five. So negative three point five plus ten equals six point five.
Does this make sense? We started below zero and warmed up a lot, so a positive answer feels right.
At ten a.m. it's six point five degrees. Real-world math, solved!