3 pens and 3 exercise books cost KSh 234, while 4 pens and 5 exercise books cost KSh 372. Find the cost of one exercise book.

Answer and explanation

Correct answer: C. KSh 60

  1. Step 1: Let a pen cost p and a book cost b: 3p + 3b = 234 and 4p + 5b = 372. Step 2. Multiply the equations so that the p terms match, then subtract to eliminate p. Step 3. This gives b = 60, and substituting back gives p = 18. Answer: KSh 60. Why not the others: KSh 18: That is the price of one pen. KSh 69: That subtracts the two bills without first making the pen terms equal. KSh 39: That divides the first bill by the total number of items, as if pens and books cost the same.

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