Thread: Simple calculation of difference in percentage

Lets assume this case. There is a voting system by which a person can be voted up or down. These are then all added up and the percentage of positive votes to the total are the favor ratio.

Ok. So Monday Alex has a favour ratio of 60% (fr1) with 10000(v1) votes.
By Friday an extra 2000 people have voted and his total favour ratio has dropped to 58% (fr2)

So friday the total number is 12000(v2)

What is the favour ratio of the 2000 (v2-v1) votes? How would you go about calculating this?

I have already tried something along the lines of dv/v1 * 1/(dfr/fr1) but doesnt seem to add up...

I am not interested in the answer as such, I am more interested in the thought process that goes into it...

Any hints welcome.

Cheers,
Taz

Well, I would set up an equation to figure out how many people voted him favorably:

, where is the number of votes cast in favor.

That would mean after the second go around:

, where in this case is the votes cast on Friday in favor of Alex, 6000 are the votes already cast in favor of Alex, and 12000 are the votes in total that have been cast since voting began.

Solving for :

, will give us an 960 favorable votes cast on Friday.

Can you then use the above to calculate the percentage of favored votes for that day?

Some times the answer is just sooooo simple ...

Thanks for helping out!