To compare two lengths, find how much longer one is than the other. Line them up at the same start and look at the extra piece. You will use Subtracting Two-Digit Numbers.
Why it works
When two things start at the same place, the longer one sticks out past the shorter one. That extra piece is the difference, and subtraction finds it: the longer length minus the shorter length.
Worked example: Ribbon and crayon
How much longer is the ribbon than the crayon?
- Ribbon: 9 cm. Crayon: 5 cm.
- $9 - 5 = 4$.
Answer: 4 centimeters longer
Worked example: Bigger numbers
A red rope is 62 inches long. A blue rope is 38 inches long. How much longer is the red rope?
- Count up from 38: +2 to 40, +20 to 60, +2 to 62.
- $2 + 20 + 2 = 24$.
Answer: 24 inches longer
Key idea
How much longer? Subtract the shorter length from the longer one. Both lengths must be in the same unit.
Common mistake
Adding the two lengths. $62 + 38 = 100$ tells how long the ropes are end to end, not how much longer one is. Check: the difference must be smaller than the longer length.
Grown-up tip: Line up two shoes, two pencils or two toy cars, and ask how much longer one is.