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The length and breadth of a rectangle is increased by 10% and 25% respectively. What is the increase in the area?

  • A.27.5%
  • B.37.5%
  • C.47.5%
  • D.57.5%

Answer: B

Both dimensions grow, so multiply the two factors.

\[ \frac{A'}{A} = (1 + 0.10)(1 + 0.25) = 1.10 \times 1.25 = 1.375 \]

\[ \text{increase} = 1.375 - 1 = 0.375 = 37.5\% \]

Adding the percentages gives 35%; the extra 2.5% is the cross term \( 0.10 \times 0.25 \), the part of the rectangle that gains in both directions at once.

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