Percentage reasoning

[carrie]

Is this right?

If inflation is rising 500 percent a year, then someone who has $10,000 worth of purchasing power in one year would need $60,000 the next to buy the same amount of stuff—500% of $10,000 plus the original $10,000. If the inflation rate continues at that level, the following year the person would need $360,000—500% of $60,000 plus the new original figure of $60,000.

Thanks!
Carol

[Walden]

Time to buy in bulk?

[Wombat]

Is this right?

If inflation is rising 500 percent a year, then someone who has $10,000 worth of purchasing power in one year would need $60,000 the next to buy the same amount of stuff—500% of $10,000 plus the original $10,000. If the inflation rate continues at that level, the following year the person would need $360,000—500% of $60,000 plus the new original figure of $60,000.

Thanks!
Carol

Looks OK at first glance. But you don't mean that inflation is rising at 500% do you? You mean it's fixed at 500%. Otherwise you'd be calculating 500% of 500% which is ..... a lot.

[djm]

I don't think you would add the original amount again. That would give you you 600%. I something doubles in value, it increases 100%. If something quintuples in value, it increases 500%. So 5 x 10,000 = 50,000.

djm

[carrie]

I something doubles in value, it increases 100%. If something quintuples in value, it increases 500%. So 5 x 10,000 = 50,000.

That was the start of the confusion. If something increases 100%, it doubles. What happens if it increases 200%, by your reasoning?

Carol

[carrie]

Is this right?

If inflation is rising 500 percent a year, then someone who has $10,000 worth of purchasing power in one year would need $60,000 the next to buy the same amount of stuff—500% of $10,000 plus the original $10,000. If the inflation rate continues at that level, the following year the person would need $360,000—500% of $60,000 plus the new original figure of $60,000.

Thanks!
Carol

Looks OK at first glance. But you don't mean that inflation is rising at 500% do you? You mean it's fixed at 500%. Otherwise you'd be calculating 500% of 500% which is ..... a lot.

Yep, you're right, that's what I mean. Thanks!

Carol

[carrie]

Time to buy in bulk?

Get your ocarinas now!

Carol

[Congratulations]

I'm an English major, so...

Have fun, everyone.

[Wombat]

I'm an English major, so...

Have fun, everyone.

Go on Congratulations. Join the numerati.

[djm]

That was the start of the confusion. If something increases 100%, it doubles. What happens if it increases 200%, by your reasoning?

Please don't do this to my pointy little head. I am arithmetically challenged. The best I can make of it is that you already have an existing value. "Per cent" means a fraction of one, one one-hundredth, to be exact. So to say something is 100% means one hundred one-hundredths, or one.

It is only when you go above 100% that you are increasing the value beyond one. So if you want to say that the value has doubled (i.e. 2), that would be 200 one-hundredths, or 200%.

Or if you wanted to say that the value has tripled (i.e. 3), that would be three hundred one-hundredths, or 300%.

etc.

djm

(ooo, my brain hurts )

[fiddleronvermouth]

That was the start of the confusion. If something increases 100%, it doubles. What happens if it increases 200%, by your reasoning?

Please don't do this to my pointy little head. I am arithmetically challenged. The best I can make of it is that you already have an existing value. "Per cent" means a fraction of one, one one-hundredth, to be exact. So to say something is 100% means one hundred one-hundredths, or one.

It is only when you go above 100% that you are increasing the value beyond one. So if you want to say that the value has doubled (i.e. 2), that would be 200 one-hundredths, or 200%.

Or if you wanted to say that the value has tripled (i.e. 3), that would be three hundred one-hundredths, or 300%.

etc.

djm

(ooo, my brain hurts )

She is saying that if your electricity bill is $100 and it increases 500% it will be $600. The key word is "increase". 500% of $100 is $500, as you have noted, but for a price increase, the new cost is added to the original cost.

[herbivore12]

From this Wikipedia article:

A percentage may be a number larger than 100; for example, 200% of a number refers to twice the number. In fact, this would be a 100% increase, while a 200% increase would give a number three times the original value. Thus one can see the relationship between percent increase and times increase.

[carrie]

From this Wikipedia article:

A percentage may be a number larger than 100; for example, 200% of a number refers to twice the number. In fact, this would be a 100% increase, while a 200% increase would give a number three times the original value. Thus one can see the relationship between percent increase and times increase.

Yes, that feels right to me, but what is the math behind it? (Note to self: read the Wikipedia article, silly.) Because if you use this formula to calculate, say 10%

10 x
___ = ____

100 $10,000

you get $1,000.


then if you substitute 200

200 x
___ = ____

100 $10,000

you get $20,000. Where is the "3 times the original value" business? That's why you have to add it to the original, no?

I get your point, djm--that was helpful, in a headache-producing kind of way!

Carol

oops, columns don't line up right. I meant those as fractions.

[Wombat]

Yes, that feels right to me, but what is the math behind it?

To calculate n00% of X.

(X times n) + X

[Bloomfield]

Convert percentages to fractions, that should make it easier:

100% = 1.0
200% = 2.0
500% = 5.0
50% = .5
1% = .01

$536 times 15% is the same as 115% of $536, which is $536 x 1.15