4 pens and 4 exercise books cost KSh 304, while 5 pens and 8 exercise books cost KSh 530. Find the cost of one exercise book.

Answer and explanation

Correct answer: B. KSh 50

  1. Step 1: Let a pen cost p and a book cost b: 4p + 4b = 304 and 5p + 8b = 530. Step 2. Multiply the equations so that the p terms match, then subtract to eliminate p. Step 3. This gives b = 50, and substituting back gives p = 26. Answer: KSh 50. Why not the others: KSh 26: That is the price of one pen. KSh 56.5: That subtracts the two bills without first making the pen terms equal. KSh 38: That divides the first bill by the total number of items, as if pens and books cost the same.

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