JAMB 2022 Mathematics · Question 35

What will be the result obtained when the numerator of 9650\frac{96}{50} is decreased by 37.5% and its denominator decreased by 20%.

Options

  1. A.1.5
  2. B.52\frac{5}{2}
  3. C.9648\frac{96}{48}
  4. D.0.5

Answer: A. 1.5

Explanation written with AI and checked against the answer key

1. Analyze the question

We are given the fraction 9650\frac{96}{50}. We need to:

  • Decrease the numerator (96) by 37.5%.
  • Decrease the denominator (50) by 20%.
  • Calculate the new fraction and simplify it to find the result.
2. Explain the concept

To decrease a value by a percentage, you subtract that percentage of the value from the original value.

  • Formula: New Value = Original Value - (Percentage ×\times Original Value)
  • Alternatively, you can multiply the original value by (100%−percentage)(100\% - \text{percentage}). For example, a 20% decrease means the new value is 80% of the original.
3. Show the solution

Step 1: Calculate the new numerator The original numerator is 96. We decrease it by 37.5%.

  • Decrease amount = 37.5% of 96=0.375×9637.5\% \text{ of } 96 = 0.375 \times 96
  • 0.375×96=360.375 \times 96 = 36
  • New numerator = 96−36=6096 - 36 = 60

Step 2: Calculate the new denominator The original denominator is 50. We decrease it by 20%.

  • Decrease amount = 20% of 50=0.20×5020\% \text{ of } 50 = 0.20 \times 50
  • 0.20×50=100.20 \times 50 = 10
  • New denominator = 50−10=4050 - 10 = 40

Step 3: Form the new fraction and simplify

  • New fraction = 6040\frac{60}{40}
  • Simplify by dividing both by 20: 60÷2040÷20=32\frac{60 \div 20}{40 \div 20} = \frac{3}{2}
  • Convert to decimal: 32=1.5\frac{3}{2} = 1.5
4. Identify the answer

Comparing our result (1.5) with the given options, it matches option A.

5. Exam Tip

When dealing with percentage decreases, remember that "decreasing by x%x\%" is the same as multiplying by (1−x100)(1 - \frac{x}{100}).

  • For the numerator: 96×(1−0.375)=96×0.625=6096 \times (1 - 0.375) = 96 \times 0.625 = 60.
  • For the denominator: 50×(1−0.20)=50×0.8=4050 \times (1 - 0.20) = 50 \times 0.8 = 40. This method is often faster and less prone to subtraction errors during the exam!

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