JAMB 2012 Mathematics · Question 22

The value of y for which 15y+15<12y+25\frac{1}{5}y + \frac{1}{5} < \frac{1}{2}y + \frac{2}{5} is

Options

  1. A.y>23y > \frac{2}{3}
  2. B.y<23y < \frac{2}{3}
  3. C.y>−23y > -\frac{2}{3}
  4. D.y<−23y < -\frac{2}{3}

Answer: C. y>−23y > -\frac{2}{3}

Explanation written with AI and checked against the answer key

To solve the inequality 15y+15<12y+25\frac{1}{5}y + \frac{1}{5} < \frac{1}{2}y + \frac{2}{5}, follow these steps:

1. Analyze the inequality

We have a linear inequality with fractions. To make the calculation easier, we should eliminate the fractions by multiplying the entire inequality by the Least Common Multiple (LCM) of the denominators (5, 5, 2, 5). The LCM is 10.

2. Clear the fractions

Multiply every term on both sides by 10: 10(15y)+10(15)<10(12y)+10(25)10 \left( \frac{1}{5}y \right) + 10 \left( \frac{1}{5} \right) < 10 \left( \frac{1}{2}y \right) + 10 \left( \frac{2}{5} \right)

Simplify each term: 2y+2<5y+42y + 2 < 5y + 4

3. Solve for yy

Group the yy terms on one side and the constants on the other. Let's move 2y2y to the right and 44 to the left: 2−4<5y−2y2 - 4 < 5y - 2y

Simplify: −2<3y-2 < 3y

Now, divide both sides by 3 to isolate yy: −23<y-\frac{2}{3} < y

This can also be written as: y>−23y > -\frac{2}{3}

4. Conclusion

Comparing our result to the given options, we find that y>−23y > -\frac{2}{3} matches option C.

Exam Tip: When working with inequalities, remember that if you multiply or divide by a negative number, you must flip the inequality sign. In this problem, we kept the coefficients positive by moving terms strategically, which helped us avoid that common pitfall!

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