Question 1180557: If the length of the base of a rectangle is increased by 20% and the length of the altitude is increased by 30%, by
what percentage is the area increased?
Answer by greenestamps(13200)   (Show Source):
You can put this solution on YOUR website!
An increase of 20% in the length means 20% of the original length is ADDED. That's the same as MULTIPLYING the length by 100%+20%=120%, or 1.2.
Similarly adding 30% to the width is the same as multiplying the width by 130%, or 1.3
Virtually all problems involving percent increases or percent decreases are worked far more easily if you think in terms of multiplying the given measurement by a factor -- e.g., 1.3 (=1.30=130%) for an increase of 40%, or 0.9 (=0.90=90%) for a decrease of 10%.
The length is increased by a factor of 1.2; the width is increased by a factor of 1.3. The area is increased by a factor of (1.2)*(1.3)=1.56; that represents and increase of 56% in the area.
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