Question

A photographer had to change the size of his cover photo. He increased the length by 30% and decreased the width by 10%. By what percent was the area of the final photo changed?

Answer 1

Answer:

• 23%

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Let the dimensions be x and y.

The area is:

• A = xy

When sides have changed we get:

• x - 30% = x - 0.3x = 0.7x
• y + 10% = y + 0.1y = 1.1y

The new area is:

• A = 0.7x * 1.1y = 0.77xy

The difference in areas is:

• xy - 0.77xy = 0.23xy

It represents 23% decrease.