Length word problems within 100
Solve word problems involving lengths within 100, using addition and subtraction with drawings and equations
What a learner can do afterwards
- Solve 'The rope is 45 cm long. I cut off 18 cm. How long is it now?'
- Draw a diagram (e.g. a ruler drawing) to represent a length word problem
- Write an equation with a symbol for the unknown to represent the problem
1 · Read
Word problems about length ask you to find a missing length. Some problems make a length longer, so you add. Others make a length shorter, so you subtract. Read the problem carefully to decide which one it is.
A ribbon is 62 cm long. Mia glues on another piece that is 15 cm long. The ribbon gets longer, so you add: 62 + 15 = 77. The ribbon is now 77 cm long.
Drawing helps. Draw a number line and mark where the length starts. To add a piece, hop forward. To cut a piece off, hop back. The number you land on is the new length, and the size of the hop is the piece.
Sometimes the missing number is the piece itself. Write it as a letter, like n. A rope is 80 cm and 55 cm is left after a cut, so 80 − n = 55. The letter stands for the piece you cut off.
Decide if the length grows or shrinks, write an equation with a symbol for the missing number, then solve it.
2 · Watch
Take it off screen
Where it sits
This opens up
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.