Concept 8 of 9
Word Problems & Estimating
Today's big idea
Clue words pick add or subtract; round the numbers to check.
'In all' means add; round 20+20=40 to check 41.
How it works
👀 What's going on?
A story full of numbers: do you add or take away?
💡 Here's the trick
Read for the action. In all or more means add; left or fewer means subtract. Round the numbers to check your answer is close.
23 birds and 18 fly in. In all means add: 23 + 18 = 41. Round check: 20 + 20 = 40, so 41 looks right.
✍️ Try it
45 sweets and 19 are eaten. Left means subtract: 45 − 19 = 26.
⚠️ Watch out
An estimate only checks your answer, it is not the exact answer.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“45 sweets, and 19 are eaten. How many are left?”
- 1
Find the clue word
“Left” means subtract.
- 2
Do the subtraction
45 − 19 = 26
- 3
Round to check
50 − 20 = 30, and 26 is close to 30, so it looks right.
- 4
Answer ✓
26 left
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Read the story and use the clue word.
23 birds sit. 18 more fly in all. How many altogether?
Does “in all” mean add or subtract?
Quick check
✅ VERIFICATION
Estimate 38 + 41 by rounding each to the nearest ten.
⚡ Finish the activity above first to answer.
Keep going!
Up next: Estimate to Check
38 + 41 is about 40 + 40 = 80.