• # question_answer If the cost of 4 books and 5 notebooks is Rs 32 and the cost of 4 notebooks and 5 books is Rs.31. The cost of each book is A)  2     B)  3     C)  4       D)  5

Let the number of books and notebooks be a and b respectively. We have, $4a+5b=32$ ?(i) and        $5a+4b=31$                 ?(ii) On multiplying Eq. (i) by 4 and Eq. (iii) by 5 and then subtracting, we get \begin{align} & \,\,16a+20b=128 \\ & \underline{\begin{align} & \,\,25a+20b=155 \\ & \,-\,\,\,\,\,\,\,-\,\,\,\,\,\,\,\,\,\,\,- \\ \end{align}} \\ & \,\,\,\,\,\,\,\,\,\,\,-9a=-27 \\ \end{align} $a=3$