Question 9 of 47intermediate⚖️ EvaluateEssay2 marks

What is 18×518 \times 5? Do you think they are all correct? Why do you think so?

Correct Answer

Answer: Yes, all methods are correct because they all give the answer 90.

Method 1: Half of 18 is 9 9×59 \times 5 = 45 9×59 \times 5 = 45 45 + 45 = 90 ∴ Answer is 90

Method 2: Double 18 to get 36 Double 36 to get 72 Add 18 to get 90 ∴ Answer is 90

Method 3: Split 18 into 8 and 10 8×58 \times 5 = 40 10×510 \times 5 = 50 40 + 50 = 90 ∴ Answer is 90

Method 4: 18×518 \times 5 = 9×109 \times 10 9×109 \times 10 = 90 ∴ Answer is 90

Method 5: 20×520 \times 5 = 100 Subtract 2×52 \times 5 = 10 100 - 10 = 90 ∴ Answer is 90

Exercise: Many Ways to Multiply | Q: 1 | (Chapter: Page 5)
For More Understanding

Explanation

The chapter demonstrates multiple strategies for multiplication: halving and doubling, splitting numbers, using friendly numbers, and compensation. All methods are mathematically valid and arrive at the same correct answer.

Solution Steps

  1. Method 1: Half of 18 is 9, so 9×59 \times 5 = 45 and 9×59 \times 5 = 45, then 45 + 45 = 90.

  2. Method 2: Double 18 to get 36, double 36 to get 72, add 18 to get 90.

  3. Method 3: Split 18 into 8 and 10, so 8×58 \times 5 = 40 and 10×510 \times 5 = 50, then 40 + 50 = 90.

  4. Method 4: 18×518 \times 5 = 9×109 \times 10 = 90.

  5. Method 5: 20×520 \times 5 = 100, subtract 2×52 \times 5 = 10, so 100 - 10 = 90.

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