Idea 9of 23Builds onMultiply first, then add
An expression in a story
How does an expression answer a real question?
Today you'll discover
- what the letter stands for in the story
- how to put in the real number
- how to check the answer makes sense
Think first5 boxes of p pencils, and 3 loose
Each box holds 12 pencils. How many pencils are there in all?
Decide first, then press Next. Find what the letter stands for in the story.
Five boxes marked p and 3 loose squares, with 5p + 3 under them. Then the boxes open to show 12 each, with p = 12, and the working 5 × 12 + 3 = 60 + 3 = 63. The last step shows four boxes of s stickers and 6 loose: 4s + 6.
See the whole ideathe big idea and the key word, in one place
The big idea
Put the real number in for the letter, and the expression gives the real total.
For exampleBus rides cost $3 each, plus $5 for the card: 3r + 5. For 4 rides, 3 × 4 + 5 = $17.
Easy to get wrongCheck that the answer makes sense: 63 pencils is about 5 boxes of a dozen, plus a few.
Key word
- formula
- an expression that works out something real, like 5p + 3 for all the pencils
Ready to use it?
- Evaluate an expression that comes from a real story.