Hi! I can not figure out how to tell to divide by the old amount or the new one... it seems to switch around and I can't see the pattern :( So here's the problem: Ashley has 92 dollars in the bank today. Yesterday, she had 286 dollars in the bank. By what percentage did Ashley's bank account decrease over the past day? (Round your answer to the nearest hundredth of a percent.) So the difference is 194 and the solution should be 194/either the old amount or the new amount, but other than just taking a guess, I don't know how to choose :(

Question

Hi! I can not figure out how to tell to divide by the old amount or the new one... it seems to switch around and I can't see the pattern :(  So here's the problem:  Ashley has 92 dollars in the bank today. Yesterday, she had 286 dollars in the bank. By what percentage did Ashley's bank account decrease over the past day? (Round your answer to the nearest hundredth of a percent.)   So the difference is 194 and the solution should be 194/either the old amount or the new amount, but other than just taking a guess, I don't know how to choose :(

shane_b · Answer

Your goal is to find out what percent of 286 is 194.  Thinking of it this way may help...if you had 100 dollars and spent 90 of it, you spent 90%.  Mathematically, that's:$$\frac{90}{100}*100=90 \%$$ So which way do you think you should do it for your problem?

anonymous · Answer

286 would be the 100, so 194/286 and times the result by 100 to put it back into percent form. Maybe I understand it a little better. I wish understanding math wasn't so hard for me.  Thank you for helping me!

shane_b · Answer

No problem at all.  Just remember, had you done it the other way (194/92) you would have ended up with 211%...which is intuitively wrong.

Always do a gut-check at the end...it will save you from a lot of silly mistakes!