# An increase of $0,15 on a price of 2,50 is an increse by a fraction 1. Nov 2, 2007 ### rkm-87 an increase of$0,15 on a price of 2,50 is an increse by a fraction of 0.15/2.50=0,06

expressed as a percentage,therefore a 6% increase

I don,t understand this

and why we put 0.15 is numerator

2. Nov 2, 2007

### symbolipoint

Decide which culture you are expressing; either a comma for whole-fraction separation, or a period, dot for whole-fraction separation. Let's use the dot, or "decimal point".

You can compare the size of price increase to the original or starting price. This comparison can be expressed as a fraction. You put the 0.15 in the numerator because you are looking at how large is the increase compared to the original; otherwise, you could compare the original price to the price increase by putting the 2.50 in the numerator.

What fraction of the original is the increase? 0.15/2.50
What fraction of the increase is the original? 2.50/0.15

Obviously, in the second case, the fraction is actually larger than 1. [two and a half over fifteen hundredths]

3. Nov 3, 2007

### rkm-87

you mean that percentage is change over the whole

4. Nov 4, 2007

### rkm-87

I have problem with concept of percentage

I don't understand it clearly

5. Nov 4, 2007

### symbolipoint

Percentage is the numerator corresponding to a denominator of 100.
0.06 = 6/100 = 6 %, meaning six percent.

6. Nov 4, 2007

### CompuChip

Or, if you would normalize it to 100, how much it would become. This allows for easy comparison.

Compare it to this example: brand A comes in 50 cl bottles and costs $0.60, brand B costs$ 0.45 but it only comes in 33 cl bottles, which one is a better buy?
One way (the most common, I think) to see this is by converting both quantities to the 1 liter price. I need to bottles of A to make a liter, so A costs $1.20 for a liter, while B costs$ 0.45 * (100 / 33) $\approx$ $1.36 per liter. So though A is more expensive, it is cheaper in comparison with B. Now take this example: in one store the salesman gives me a$ 200 discount on a TV which would normally cost $1500, in another store I find a cheaper TV of$ 1300 but I only get $125 discount. In which store will I relatively save the most money? Again, we normalize the price of a TV to$ 100. Dividing the price and the discount by 15 on both sides, I would get about $13.33 off at one, and (divide by 13)$9.62 at B, if the TV would cost $100. In other words, for each$100 dollar I would spend on the TV, I would get $13.33 discount at one store, and$9.62 at the other one. This is what we mean by saying "I get a 13.33% discount at one store, and 9.62% at the other" (x % being: x on every 100).