The cost of 6 pens and 3 pencils is ₹ 84. One-third of the cost of one pen is equal to the cost of one pencil. What is the total cost of 4 pens and 5 pencils?
(a)₹ 66
(b)₹ 68
(c)₹ 72
(d)₹ 78
(e)None of these
Answer
Answer (as printed): B
Explanation
Let the cost of one pen be ₹ $x$. Then, cost of 1 pencil $$\begin{aligned} & =₹\left(\frac{x}{3}\right) . \\ & \therefore \quad 6 x+3 \times \frac{x}{3}=84 \Rightarrow 7 x=84 \Rightarrow x=12 . \end{aligned}$$ So, total cost of 4 pens and 5 pencils $$=₹\left(4 x+\frac{5 x}{3}\right)=₹\left(\frac{17 x}{3}\right)=₹\left(\frac{17 \times 12}{3}\right)=₹ 68 .$$
Explanation as extracted from the printed page; notation may be imperfect.