Math Heuristics for Problem Solving
Primary 3 Assumption & Its Method
What is Assumption in Math?
Assumption math problems require students to make an educated guess or hypothesis about a certain situation or scenario. In other words, they need to make an assumption based on the given information to solve the problem. These types of problems often involve figuring out missing or unknown quantities by using logic and common sense.
The Assumption method is a problem-solving strategy also known as the Supposition method. It is useful when a word problem provides the values of both items, the total quantity, and the total value. In such cases, both the Assumption or Guess-and-Check method can help find the solution.
How to Solve Math Questions with Assumption Method?
Let's take a look at this Primary 3 word problem example:
Ronald bought 8 pens and rulers for $21. Each pen cost $3 and each ruler cost $2. How many pens did Ronald buy?
Identify the Concept
The question has 2 values and 2 totals, the total quantity and the total value. Both Assumption and Guess and Check methods can works for this scenario.
Workings Explained
- The Total Quantity → 8 pens and rulers
- The Total Value → $21 (The total amount Ronald paid for all the pens and rulers)
- 2 Values → 1 Pen cost $3, 1 Ruler cost $2.
The question asks for the number of pens Ronald bought, hence we assume all are rulers.
Assume all are rulers:
8 (rulers) × 2 (value of 1 ruler) = 16 (amount paid for 8 rulers)
Total value difference (the total value difference between what was provided and what we assume):
21 (Ronald paid $21) – 16 (amount paid for 8 rulers) = 5.
Value difference (the cost difference between 1 pen and 1 ruler):
3 – 2 = 1
Number of pens:
5 (total value difference) ÷ 1 (value difference) = 5
Check
✓ Number of ruler : 8 – 5 = 3
✓ Cost of 5 pens : 5 × 3 = 15
✓ Cost of 3 rulers : 3 × 2 = 6
✓ Total paid : 15 + 6 = 21