# Math Help - Percentage question

1. ## Percentage question

Hi, I've been doing some practice papers to revise for my Biology exam (tomorrow! ) and I came accross one question about percentages...I thought it was alright at first, but looked at the mark scheme and apparently I was wrong.

Anyway, the question was:
Calculate the percentage difference between the concentration of Potassium ions in the culture solution at the start of the experiment (8.0) and the concentration of potassium ions in the barley solution (42.0)

According to the mark scheme I had to first do 42-8. Which I did, and got 34. But thats where I get stuck!
It says that the answer to the question is 425%. But how on earth did they work that out? is there even such a thing as 425%??? lol

2. Originally Posted by trishymac
Hi, I've been doing some practice papers to revise for my Biology exam (tomorrow! ) and I came accross one question about percentages...I thought it was alright at first, but looked at the mark scheme and apparently I was wrong.

Anyway, the question was:
Calculate the percentage difference between the concentration of Potassium ions in the culture solution at the start of the experiment (8.0) and the concentration of potassium ions in the barley solution (42.0)

According to the mark scheme I had to first do 42-8. Which I did, and got 34. But thats where I get stuck!
It says that the answer to the question is 425%. But how on earth did they work that out? is there even such a thing as 425%??? lol
yes, there is a thing as 425%. it just means you have 4 and one quater times what you've started with. we started with 8 and increased to 42, now we have to find what the percentage increase is, which is the same as the percent difference between the two.

whenever we want to know what percentage of the original number a number is, we put the new number over the old number and multyply by 100.

So percentage increase $= \frac {amount \mbox { } of \mbox { } increase}{original \mbox { } amount} \times 100$

Now try to see if you can get the answer

3. i got it! thank you!!