Lesson 3.5 · Adding and Subtracting Within 100
One- and two-step word problems
Word problems tell a math story. Your job is to find out what is happening. Then you pick: add or subtract? Some stories have two parts, so you do two steps.
Read, think, solve
- Read the story. What do you need to find?
- Think. Are things put together or added on? Add. Are things taken away? Subtract. Are two amounts compared? Subtract to find the difference.
- Solve and check. Does your answer make sense?
Add or subtract?
- Joining or putting together: add.
- Taking away or finding what is left: subtract.
- "How many more?" or "How many fewer?": subtract the smaller number from the bigger one.
Worked example: One step: putting together
Leo has 34 stickers. His sister gives him 28 more. How many stickers does Leo have now?
He gets more, so add: 34 + 28.
Ones: 4 + 8 = 12. Write 2, move 1 ten. Tens: 3 + 2 + 1 = 6.
Leo has 62 stickers.
Worked example: One step: comparing
Ava jumped rope 71 times. Ben jumped 45 times. How many more times did Ava jump?
Compare, so subtract: 71 − 45.
71 is 6 tens and 11 ones. Ones: 11 − 5 = 6. Tens: 6 − 4 = 2.
Ava jumped 26 more times.
Worked example: Two steps
A bakery has 50 muffins. It sells 26. Then it bakes 18 more. How many muffins does it have now?
Step 1: Sold means take away. 50 − 26 = 24.
Step 2: Baked more means add. 24 + 18 = 42.
The bakery has 42 muffins.
Common mistake
Don't just grab the numbers and add. Read the whole story first. "How many more" sounds like adding, but you subtract to compare.
Tip
Draw a quick picture or a bar. Put the parts you know in the bar. The missing part is what you solve for.
Practice
There are 27 kids on the bus. At the next stop, 35 more kids get on. How many kids are on the bus now?
Type a number.
Nora has 64 marbles. She loses 29. How many marbles does she have left?
Type a number.
A red ribbon is 82 inches long. A blue ribbon is 57 inches long. How many inches longer is the red ribbon?
Type a number.
A farm has 24 cows, 31 pigs and 19 goats. How many animals is that in all?
Type a number.
Omar had some shells. He found 16 more. Now he has 43 shells. How many shells did he have at the start?
Type a number.
Ella picked 45 apples. Her dad picked 38 apples. They used 20 apples to make pies. How many apples are left?
Type a number.
A book has 90 pages. Jay reads 34 pages on Monday and 28 pages on Tuesday. How many pages does he still have to read?
Type a number.
Kim has 53 beads. Tom has 18 fewer beads than Kim. Which shows how to find how many beads Tom has?