JAMB 2015 Mathematics · Question 11

Simplify 1¼ ÷ (2 ÷ ¼ of 28)

Options

  1. A.1 38 \frac{3}{8}
  2. B.2 34 \frac{3}{4}
  3. C.4 38 \frac{3}{8}
  4. D.3 15 \frac{1}{5}

Answer: C. 4 38 \frac{3}{8}

Explanation written with AI and checked against the answer key

To solve this expression, we must follow the BODMAS rule, which dictates the order of operations: Brackets, Of, Division, Multiplication, Addition, and Subtraction.

1. Analyze the Expression

The expression is: 114÷(2÷14 of 28)1\frac{1}{4} \div (2 \div \frac{1}{4} \text{ of } 28)

First, convert the mixed fraction to an improper fraction: 114=541\frac{1}{4} = \frac{5}{4}

2. Solve inside the bracket

According to BODMAS, we handle "Of" before "Division" inside the bracket.

  • Step A: Solve "Of" 14 of 28=14×28=7\frac{1}{4} \text{ of } 28 = \frac{1}{4} \times 28 = 7
  • Step B: Solve the Division inside the bracket Now the bracket becomes: (2÷7)(2 \div 7) 2÷7=272 \div 7 = \frac{2}{7}
3. Complete the final division

Now substitute the result back into the main expression: 54÷27\frac{5}{4} \div \frac{2}{7}

To divide by a fraction, we multiply by its reciprocal: 54×72=5×74×2=358\frac{5}{4} \times \frac{7}{2} = \frac{5 \times 7}{4 \times 2} = \frac{35}{8}

4. Convert to a mixed fraction

Divide 35 by 8: 35÷8=435 \div 8 = 4 remainder 33 So, 358=438\frac{35}{8} = 4\frac{3}{8}

Conclusion

Comparing our result to the options provided: A. 1381\frac{3}{8} B. 2342\frac{3}{4} C. 4384\frac{3}{8} D. 3153\frac{1}{5}

The calculated value matches option C.

Exam Tip: Always remember that in BODMAS, "Of" acts like multiplication but takes precedence over standard division. If you had divided 2 by 1/4 first, you would have gotten the wrong answer. Always look for the "Of" and solve it immediately!

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