Bigger numbers do not change the thinking. Draw the bars and find the missing piece.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Guess before you work
For 486 − 253, the answer is near 200. If you get 700, something is wrong.
Check at the end
Add your answer back, or ask whether it makes sense in the story.
Bigger numbers, unchanged thinking
A word problem with 348 and 175 asks the same kind of question as one with 8 and 5. Draw the bar model, decide whether you are combining or comparing, then do the arithmetic. Do not let the size of the numbers change how you read the story.
Estimate before you calculate
With three-digit numbers an estimate is more valuable, because a slipped digit changes the answer by a lot. 348 + 175 is roughly 350 + 175 = 525, so expect something in the five hundreds. Now the exact calculation has something to be measured against.
Ask whether the answer makes sense
If a school has 348 pupils and 175 more join, an answer of 173 is impossible — the school grew, so the number must be larger. Checking the direction of change catches errors that arithmetic checking sometimes misses.
Step 2: Try It Yourself
Tap and try it out.
First amount and Second amount
234
152
In all
386
234 and 152 make 386.
Step 3: Watch an Example
One step at a time.
Watch Leo Estimate First
A shop had 486 items and sold 253.
- Step 1
He rounds in his head: about 500 take about 250.
Step 4: Your Turn
Practice makes it stick.
The Football Match
Problem 1 of 3
345 adults and 268 children came to a match. How many people came?
people
The Book Drive
Problem 2 of 3
A target of 500 books has 236 collected. How many more are needed?
books
Two Steps
Problem 3 of 3
A shop had 420 items, got 175 more, then sold 260. How many now?
items
Work It Out
1 of 3
318 + 245 = ?
2 of 3
604 − 271 = ?
3 of 3
250 more than 375 is?
Step 5: Quick Check
Show what you know.
Question 1 of 2
462 + 289 = ?
Question 2 of 2
Why estimate before working it out?
What You Learned
- Bigger numbers do not change the thinking.
- Estimate first, so a wrong answer stands out.
- Check at the end by adding back.