Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

I know this seems like a juvenile question, but for some reason I can't recall how to do this.

Lets say I want to find 87 reduced by 99.75%. What is the equation to do that?

Thanks!

share|improve this question
1  
See my answer to this similar question here math.stackexchange.com/questions/14715/… –  Bill Dubuque Dec 20 '10 at 17:24
add comment

2 Answers

up vote 4 down vote accepted

A simple formula for this is: $$ \text{ New Number } = \text{ Old Number } \times \left(\frac{100 - x}{100}\right)$$

In general if a number is increased or decreased by $x\%$ then the new number is given by: $$ \text{ Old Number } \times \left(\frac{100 \pm x}{100}\right)$$

share|improve this answer
    
This is what I remember as the formula I was looking for! Thanks –  Dream Lane Dec 20 '10 at 19:45
add comment

If you want $X$% of 87, multiply the latter by $\frac{X}{100}$. (So, for example, to get 25 percent, you multiply by $0.25$).

If by "reduced by 99.75%" you mean 99.75% of the total, then, multiply by $.9975$. If "reduced by 99.75%" means taking 99.75% off (so you are left with only 0.25%), then multiply by $0.0025$.

share|improve this answer
    
Great answer! Very informative, thank you –  Dream Lane Dec 20 '10 at 19:45
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.