2020 · Q72
The length of a rectangle is increased by 10% and breadth is decreased by 10%. Then the area of the new rectangle is
Elementary MathematicsPercentages
- Aneither increased nor decreased
- Bincreased by 1%
- Cdecreased by 1%
- Ddecreased by 10%
Explanation
Take the original area as 1 unit. The new length is 1.10 and the new breadth is 0.90 of the original, so the new area is 1.10 × 0.90 = 0.99. That is 1% less than the original area. The trap is assuming equal-and-opposite changes cancel — multiplication is not addition, so a 10% rise followed by a 10% fall always leaves slightly less than 100%. Hence option (C) decreased by 1%.