josemnz83 wrote:

I solved this question by cross multiplying.

15*10^-4m=15*10^-14k

-4m-14k=0

-4(7)-14(-2)=0

-28+28=0

m-k

7-(-2)= 9

Hello josemnz84 - I was looking at the alternate ways to solve this problem and I don't quite understand what you did here. Can you please explain? Specifically how did you get \(10^{-14k}\). I feel this is incorrect, but please correct me if my calculations are off.

If you want to cross multiply, the problem would be done this way:

\(\frac{15*10^{-4 + m}}{3*10^{-2+k}} = 5*10^7\)

\(15*10^{-4 + m}=15*10^{5 + k}\) - when you multiple powers of 10, you multiply the whole numbers and add the powers of 10 (you seemed to have multiplied the exponents rather than adding to get 10^-14 in your answer). See this:

http://www.dummies.com/how-to/content/m ... ation.htmlAfter cancelling out the "15 x 10^" (essentially 10^1) from both sides, you are left with:

\(-4 + m = 5 + k\)

\(m - k = 5 + 4\)

\(m - k = 9\)

Answer: A~ Im2bz2p345