Many real problems need two or three steps. You now have every tool: the four operations, what to do with a remainder, and rounding to estimate.
Idea clave
Plan before you calculate: What is the question? What do I need to find first? Write each step as its own equation, using a letter for the unknown if it helps. When you finish, check with an estimate.
Por qué funciona
A long problem is a chain of short ones. Each step uses the answer to the step before it. Writing the steps keeps the chain in order, and an estimate catches a step that went wrong.
Ejemplo resuelto: Buy, then find what is left
Mia has \$145. She buys 3 books that cost \$18 each. How much money does she have left?
- First the cost of the books: $3 \times 18 = 54$.
- Then what is left: $145 - 54 = m$, so $m = 91$.
- Estimate: $3 \times 20 = 60$ and $150 - 60 = 90$. Close to 91.
Respuesta: \$91
Ejemplo resuelto: Three steps with a remainder
125 students and 9 adults go on a trip. Each bus holds 40 people. How many buses are needed?
- People in all: $125 + 9 = 134$.
- $134 \div 40 = 3$ R 14.
- The 14 extra people need a bus, so add one more.
Respuesta: 4 buses
- Read the whole problem and underline the question.
- Find what you need first, one step at a time.
- Decide what a remainder means.
- Check with an estimate: is the answer about the right size?