If $5$ pens and $8$ books cost Rs. $290$, and $5$ pens and $4$ books cost Rs. $170$, the cost of $1$ book is:

If $5$ pens and $8$ books cost Rs. $290$, and $5$ pens and $4$ books cost Rs. $170$, the cost of $1$ book is:
  1. Rs. $25$
  2. Rs. $28$
  3. Rs. $30$
  4. Rs. $32$

Solution

Subtract: $(5p + 8b) - (5p + 4b) = 290 - 170 \Rightarrow 4b = 120 \Rightarrow b = $ Rs. $30$.

Asked in: IMO

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