Make Assumption

One of the many heuristics for Primary Math question in SG

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How to Solve by Assumption

We make an assumption (or a guess) and then check the result. If it doesn’t match, we adjust.

Example 1: Chickens & Rabbits

A farmer has 42 animals in total. He counted 110 legs.

Step 1: Assume all 42 are chickens (2 legs each). Total legs = 42 × 2 = 84.

Step 2: But we need 110 legs. Difference = 110 − 84 = 26 legs.

Step 3: Each rabbit has 2 extra legs compared to chicken. So number of rabbits = 26 ÷ 2 = 13.

Step 4: Chickens = 42 − 13 = 29.

Answer: 29 chickens, 13 rabbits ✅

Example 2: Bicycles & Tricycles

A shop has 30 bicycles and tricycles. Total wheels = 80.

Step 1: Assume all 30 are bicycles (2 wheels each). Total wheels = 60.

Step 2: Actual is 80. Difference = 20.

Step 3: Each tricycle has 1 extra wheel. So number of tricycles = 20 ÷ 1 = 20.

Step 4: Bicycles = 30 − 20 = 10.

Answer: 10 bicycles, 20 tricycles ✅

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