Money and measurements are full of decimals. You can add, subtract, multiply and divide them, and you can check with an estimate and divide by a decimal. A word problem puts those skills in order.
Key idea
Read the problem and decide what each step finds. Write the operation for each step, estimate, compute carefully with the points lined up or counted, and check that the answer fits the story.
Why it works
Each operation matches an action: putting amounts together is adding, finding what is left or how much more is subtracting, equal groups is multiplying, and sharing or fitting pieces is dividing. Decimals do not change the meaning of the operations, only the arithmetic.
Worked examples
Worked example: Two steps with money
Ana buys 3 notebooks at \$2.45 each and a pen for \$1.20. She pays with a \$10 bill. How much change does she get?
- Notebooks: $3 \times 2.45 = 7.35$.
- Add the pen: $7.35 + 1.20 = 8.55$.
- Change: $10.00 - 8.55 = 1.45$.
- Estimate: $3 \times 2.5 + 1 = 8.5$, so about \$1.50 change. It fits.
Answer: \$1.45
Worked example: How many pieces?
A ribbon is 4.5 m long. How many 0.75 m pieces can be cut from it?
- How many 0.75s fit in 4.5? Divide: $4.5 \div 0.75$.
- Multiply both by 100: $450 \div 75 = 6$.
- Check: $6 \times 0.75 = 4.5$.
Answer: 6 pieces
Common mistake
Picking the operation from the numbers instead of the story, such as multiplying $4.5 \times 0.75$ because the numbers are decimals. Ask what the story does: cutting pieces from a length is dividing. Then check that the answer makes sense: 3.375 pieces would be odd.