asfandabid wrote:

We can also solve this by using the formula

a+b+(a*b)/100

=(-15)+(40)+(-15*40)/100

=25-6

=19%

which is positive so it represents a 19% increase.

D is the answer

asfandabid, this shortcut looks handy. Clearly it's a percent change formula, but its elements and operations in the numerator aren't clear to me.

(Yes, I see that you've taken Change 1 of a side, added Change 2 of another side, then added the product of the two. Why? I'm having a hard time wrapping my mind around the idea that you would account separately for each one-dimensional change, add them, then account for a two-dimensional change, and add that on. And are you assuming original values of 100 per side?)

Please explain the formula? Perhaps you could write out the elements in the numerator and explain why the operators work as they do? Thanks in advance.

_________________

In the depths of winter, I finally learned

that within me there lay an invincible summer.

-- Albert Camus, "Return to Tipasa"