Subtracing a percentage

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Jschoon4

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Nov 2, 2012
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Ex. I have 163.47 and I need to subtract 3.75%

Currently I have subtracted 163.47*.0375 = 6.13-163.47=157.34
I also tried 163.47 * .9625 = 157.34

Q) Why or How is that both of these answers when I "Add" 3.75% back into them do not equal my original value of 163.47

That guess I came up with, with no rounding the correct answer is 157.56 becasue you add 157.56+3.75 = 163.47

Any ideas
 
Jschoon4 said:
Ex. I have 163.47 and I need to subtract 3.75%

Currently I have subtracted 163.47*.0375 = 6.13-163.47=157.34
I also tried 163.47 * .9625 = 157.34

Q) Why or How is that both of these answers when I "Add" 3.75% back into them do not equal my original value of 163.47

That guess I came up with, with no rounding the correct answer is 157.56 becasue you add 157.56+3.75 = 163.47

Any ideas
Click to expand...

Can you please state exactly what the problem is asking? It's tough to figure out what needs to be done based on what you stated.
 
srmichael said:
Can you please state exactly what the problem is asking? It's tough to figure out what needs to be done based on what you stated.
Click to expand...

**I need for when you add 3.75% back in to the Sum/total of 163.47-3.75% to equal original value of 163.47 not 163.24

Ex. 163.47-3.75% = 157.34 but when you take 157.34+3.75 it equals 163.24 when it should equal 163.47
 
Jschoon4 said:
**I need for when you add 3.75% back in to the Sum/total of 163.47-3.75% to equal original value of 163.47 not 163.24

Ex. 163.47-3.75% = 157.34 but when you take 157.34+3.75 it equals 163.24 when it should equal 163.47
Click to expand...
I suspect English is not your native language. Is that correct?

\(\displaystyle 163.47 * 0.0375 = 6.130125.\) Correct?

\(\displaystyle 157.339875 * 0.0375 = 5.9002453125 < 6.130125.\) Correct?

\(\displaystyle If\ a < b\ and\ c > 0,\ then\ a * c < b * c.\) Correct?

When you subtract 3.75% of 163.47 from 163.47, you get a number smaller than 163.47 so 3.75% times that smaller number will never equal 3.75% times 163.47. Make sense now?
 
Tithe

My church teaches that I should give 10% of my income to God before I use any of it for another purpose,

Bill is willing to give me 10% if I loan it to him for one day.

Bill is NOT willing to pay me the same interest as God got, because the amount was smaller when it got to him.


Answer:
10% of something. Is a different for different somethings.

If I get $100 on payday then 10% of $100 = $10 (to God)
Bill gets $90 and will only pay 10% of $90 = $9 (to me)

I get $99 tomarrow. God took 10% Bill gave back 10%, I'm still a dollar short, but going to heaven:)

(please don't tell God about the $9 that I made on-the-side)
 
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Hello, Jschoon4!

You've fallen into the trap of a classic trick question.

I have 163.47 and I need to subtract 3.75%

Currently I have subtracted: (163.47)(0.0375) = 163.47 - 6.13 = 157.34 . Yes!
I also tried: (163.47)(0.9625) = 157.34 . Right!

Q) Why or how is that both of these answers, when I "Add" 3.75% back into them,
do not equal my original value of 163.47 ?
Click to expand...

The percent of increase is not equal to the percent of decrease.

The percent of change is based on the starting number.


Suppose an item sells for $500.
It is on sale with a \(\displaystyle \color{red}{20\%}\) discount.

Since \(\displaystyle (\$500)(0.20) = \$100\), the sale price is: \(\displaystyle \$500 - 100 \:=\:\$400\)


After the sale, you want to restore the original price.
You must raise $400 to $500 . . . a $100 increase.

But this is a: .\(\displaystyle \dfrac{100}{400} = \color{red}{25\%}\) increase.

Get it?
 
mmm4444bot said:
I am glad that you get it now, but why did you write the false equation above? :cool:
Click to expand...

? I didn't write that equation. Mine is 163.47 -3.75%

So, lets say the markup on an item is 3.75% How do you figure the base cost? Let s say 163.47 is the price but that is with a 3.75% markup. What's the Base cost?
 
Jschoon4 said:
? I didn't write that equation. Mine is 163.47 -3.75%

So, lets say the markup on an item is 3.75% How do you figure the base cost? Let s say 163.47 is the price but that is with a 3.75% markup. What's the Base cost?
Click to expand...
If you know algebra, it is easy to get the answer.

\(\displaystyle Let\ b = the\ base\ cost.\)

\(\displaystyle Let\ m = the\ \text{mark-up} \ percentage.\)

\(\displaystyle Let\ p = the\ sales\ price.\)

\(\displaystyle Then\ p = b + (\frac{m}{100} * b) = b(1 + \frac{m}{100}) = b * \dfrac{100 + m}{100}.\)

Given any two variables, you can calculate the third.

\(\displaystyle p = b * \dfrac {100 + m}{100}.\)

\(\displaystyle b = \dfrac{100 * p}{100 + m}.\)

\(\displaystyle m = \dfrac{100(p - b)}{b}.\)
 
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JeffM said:
If you know algebra, it is easy to get the answer.

\(\displaystyle Let\ b = the\ base\ cost.\)

\(\displaystyle Let\ m = the\ \text{mark-up} \ percentage.\)

\(\displaystyle Let\ p = the\ sales\ price.\)

\(\displaystyle Then\ p = b + (\frac{m}{100} * b) = b(1 + \frac{m}{100}) = b * \dfrac{100 + m}{100}.\)

Given any two variables, you can calculate the third.

\(\displaystyle p = b * \dfrac {100 + m}{100}.\)

\(\displaystyle b = \dfrac{100 * p}{100 + m}.\)

\(\displaystyle m = \dfrac{100(p - b)}{b}.\)
Click to expand...

Your asking me to muliply "b" in your formula which in this case you have as your base price. Correct
How do I do that when I don't know the base cost is? You're saying this formula will give me my answer of the base cost? even though I don't know what "b" is?
 
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Jschoon4 said:
Your asking me to muliply "b" in your formula which in this case you have as your base price. Correct
How do I do that when I don't know the base cost is? You're saying this formula will give me my answer of the base cost? even though I don't know what "b" is?
Click to expand...
If you look at the bottom of my previous post, you will see THREE related formulas. You choose the one that is right for your problem. You want to find b so you pick the one that has b on the left and fill in the numbers for p and m on the right. That gives you b. If you knew b and p and wanted to know m you would choose the formula that has m on the left and fill in the numbers for b and p on the right.
 
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