Math 7 · Unit 3, Lesson 7: Rational Number Problems · Tile 2 of 4
Plan It Out
Write one expression, estimate, then solve
Make a plan
Real problems with several steps are easier with a plan. First, give every number a sign that matches the story. Second, write the whole problem as one expression. Third, estimate with friendly numbers. Fourth, solve it in order. Last, check that your answer is close to your estimate.
- Sign it
- Write it
- Estimate it
- Solve it
- Check it
Represent the situation with a single numerical expression, estimate its value, then evaluate it and compare.
One expression for the whole story. A quick guess first. Then the real answer, and see if they match.
Watch it work
Bake sale. The class buys 3 bags of flour at $4.29 each and sells 48 cookies at $0.75 each. What is the profit?
- Sign it. Buying is negative, selling is positive.
- Write it. 48 × 0.75 + 3 × (−4.29)
- Estimate it. 48 × 0.75 is about 36, and 3 × 4 is 12, so about 24.
- Solve it. 36 + (−12.87) = 23.13
- Check it. $23.13 is close to 24.
The profit is $23.13.
NC standard: NC.7.NS.3.