Kelly enlarged the area of a photograph to 250% of its original size. The original dimensions of the photograph were 5 inches by 7 inches. What is the area of the enlarged photograph, in square inches?

Question

I know the solution is 5(2.5) times 7(2.5) but it says she enlarged the area by 250 percent. so shouldn't it be 2.5 (35)?

Also when do we know when to add 100% to a percent or keep it as the percent like this question? please help

Answer 1

you are correct

when something is "increased by" 20%, that means it has an extra 20%, or 1.2 times its value

when they give you an actual size factor, there's no additional 100% to add.
Many people get these confused, so make sure to read the question carefully.

Answer 2

Also, the "solution" you cite would be correct if the photograph had been enlarged by a factor of 250%. In that case, it usually means that each dimension is increased, not the area. So your analysis is correct, if the question was worded correctly.

Answer 3

Oh so since it's the area then it would have to be 5(2.5) times 7(2.5) ?

Answer 4

Depends.
If, as stated, the area grew to 250%, then it becomes 2.5(35)
If both length and width were magnified by a factor of 2.5, then yes, 5(2.5) * 7(2.5) = 35 * 2.5^2