Stuart sells a pen to Sandy at a profit of 25%. Sandy sells it to Andy at a profit of 10% and Andy sells it to Keith at a profit of 5%. If Andy sells it for Rs. 231, find the cost price at which Stuart bought the pen?

Using the successive selling price formula, the final selling price equals the original cost price multiplied by (1 plus Profit 1 in decimals) multiplied by (1 plus Profit 2 in decimals) multiplied by (1 plus Profit 3 in decimals). Substituting the given values gives 231 equals Cost Price times 1.25 times 1.10 times 1.05. This simplifies to 231 equals Cost Price times 1.44375. Dividing 231 by 1.44375 yields Rs. 160, which is the cost price at which Stuart bought the pen.

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