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Concept 5 of 8

Measurement Word Problems

1

Today's big idea

Matching the units is a step of its own, done before you add or subtract.

Word problems hide the conversion; nothing in them tells you to do it.

2

How it works

👀 What's going on?

A word problem never says "now convert". It hands you 1 L 200 mL and 350 mL and expects you to notice that they do not match. That mismatch is easy to miss.

💡 Here's the trick

Same unit first. Then add or subtract.1 L 200 mL−350 mL=850 mLleft in jugStep 1: 1 L 200 mL → 1,200 mLStep 2: 1,200 − 350 = 850 mL ✓

Look at the jug above. It holds 1 L 200 mL, and 350 mL is poured out. You cannot take 350 away from 1, because those two numbers count different things. Step 1 rewrites 1 L 200 mL as 1200 mL. Only then does step 2 work: 1200 − 350 = 850 mL. Matching the units is a step of its own.

🪄 How to do it

  1. 1.Read the two amounts on the jug above, with their units.
  2. 2.If the units differ, rewrite both in the smaller unit.
  3. 3.Decide add or subtract from the story, then work it out.

✍️ Try it

  1. 1.Two ribbons are 1 m 20 cm and 75 cm long. Joined end to end, how long are they?
  2. 2.A jar of jam weighs 1 kg 200 g. The empty jar weighs 450 g. How heavy is the jam inside?

The ribbons: 1 m 20 cm is 120 cm, and 120 + 75 = 195 cm, so 1 m 95 cm. The jam: 1 kg 200 g is 1200 g, and 1200 − 450 = 750 g of jam.

⚠️ Watch out

You might be thinking the word "more" always means add. It does not. A bag 300 g heavier than 2 kg needs adding, but asking how much more a tank holds needs subtracting. Picture the story instead of hunting for a word.

🌟 Why this matters

Shopping, cooking, and packing are word problems you already solve without calling them that. You work out whether 900 g of rice fits a 1 kg tin, or whether two ribbons reach across a window. Matching the units first is what keeps your answer sensible.
Exam tip: Underline both units, rewrite them in the smaller one, then touch the numbers.

3

Watch me solve one

Quanta solves it

“Watch how I think through one of these — then you try.”

THE PROBLEM

“A rope is 3 m long. 80 cm is cut off. How much rope is left?”

  1. 1

    Make units MATCH

    Convert 3 m to all cm: 300 cm. ⚗️

  2. 2

    Pick the operation

    "Cut off" → subtract.

  3. 3

    Subtract

    300 − 80 = 220

  4. 4

    Answer ✓

    Left: 220 cm = 2 m 20 cm

Now you try one — same steps, different story 👇

4

See it in action

⚡ Time to play!

Read the clue words, then tap the operation they point to.

PROBLEM 1 OF 3

A ribbon is 240 cm long. Meena cuts off 90 cm. How much is left?

Which operation?

5

Quick check

✅ VERIFICATION

Three shelf pieces are needed, each 45 cm long. Your plank is 1 m 50 cm. Is there enough wood?

⚡ Finish the activity above first to answer.

Keep going!

Up next: Thermometer

Read the mercury level, then do the change.

Concept 6 of 8 →