math Homework help? 15% of 40 ?

[Froody129]

Although this is a very simple problem, I always break it up into powers of 10.

 

So in 40 we have 4 10's. What's 15% of 10? Easy, 1.5. 1.5x4=6.

[RGProductions]

4 hours ago, echy said:

never mind i found the answer 15 divided by 100 = 0.15

sorry bout that. i answered already

15% is 15/100, which is 0.15

[Dash Lambda]

5 hours ago, djdwosk97 said:

Percents confuse a lot of people. 

They shouldn't though.

I'm not saying anyone who doesn't get them is an idiot, but there is definitely some exceptional factor. I'd say it's that they, from most to least likely, were poorly taught, are very young, or are mentally challenged in some way (I've only ever met one person who fit the last one).

 

Reason being, since "per" indicates division, "of" indicates multiplication, and "cent" is a number, "X percent of Y" is literally the mathematical expression you use. Every time you say it, you're reciting instructions on how to handle it.

 

I guess it could also be that English isn't the person's first language (if they know it at all), in which case the phrase might not be so explicit.

[Syntaxvgm]

First you convert 40 to base 2, otherwise known as binary 

Here's a chart for numbers under 256

Essentially, you work from right to left, starting at 1 and doubling each time. You start on the largest column that will fit in your number, in this case 32 in column 6. That means our binary representation of 40 will be 6 bits long. 

32        16          8           4           2           1

0     |     0     |     0     |     0     |     0     |     0

Take the 32 out, leaving a 1 in that slot. 8 Remains. Move right.

32        16          8           4           2           1

1     |     0     |     0     |     0     |     0     |     0

Can you take 16 out? No you cannot, so leave a 0 there. Move right.

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

You can take 8 out. Leave one in that slot, and since that leaves you with, it's 0 for the remaining slots. 

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

 

This is now 40, converted from base 10 (Decimal) to Base 2 (Binary)

101000

 

Now, since this is irrelevant to the problem we're solving, we convert it back to decimal. 

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

32   +    0     +    8    +    0     +    0     +     0     =     40

 

Since we need 15% of 40, the way to do it on a calculator would be to represent the percentage as a part of 1, as in 100% = 1. So 15% would be 0.15. 

You now multiply 40 by 0.15. However, if you don't have a calculator or scratch paper, that might be difficult to do in your head. You know that's easy? 10s.

So multiply both 40 and 0.15 by 100. 

you get 4,000 and 15. Now multiply the two. 

4,000 * 15 = 60,000

 Now since you multiplied both side by 100, you need to divide it by the product of both. 

100 * 100 = 10,000

Now divide the result from before by this new number 

60,000  / 10,000 = 6

 

The answer is 6. 

 

[christianled59]

5 minutes ago, Syntaxvgm said:

First you convert 40 to base 2, otherwise known as binary 

Here's a chart for numbers under 256

Essentially, you work from right to left, starting at 1 and doubling each time. You start on the largest column that will fit in your number, in this case 32 in column 6. That means our binary representation of 40 will be 6 bits long. 

32        16          8           4           2           1

0     |     0     |     0     |     0     |     0     |     0

Take the 32 out, leaving a 1 in that slot. 8 Remains. Move right.

32        16          8           4           2           1

1     |     0     |     0     |     0     |     0     |     0

Can you take 16 out? No you cannot, so leave a 0 there. Move right.

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

You can take 8 out. Leave one in that slot, and since that leaves you with, it's 0 for the remaining slots. 

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

 

This is now 40, converted from base 10 (Decimal) to Base 2 (Binary)

101000

 

Now, since this is irrelevant to the problem we're solving, we convert it back to decimal. 

32        16          8           4           2           1

1     |     0     |     1     |     0     |     0     |     0

32   +    0     +    8    +    0     +    0     +     0     =     40

 

Since we need 15% of 40, the way to do it on a calculator would be to represent the percentage as a part of 1, as in 100% = 1. So 15% would be 0.15. 

You now multiply 40 by 0.15. However, if you don't have a calculator or scratch paper, that might be difficult to do in your head. You know that's easy? 10s.

So multiply both 40 and 0.15 by 100. 

you get 4,000 and 15. Now multiply the two. 

4,000 * 15 = 60,000

 Now since you multiplied both side by 100, you need to divide it by the product of both. 

100 * 100 = 10,000

Now divide the result from before by this new number 

60,000  / 10,000 = 6

 

The answer is 6. 

 

Hahaha this made my day. And if OP reads this, you just ruined his. 

[Syntaxvgm]

Just now, christianled59 said:

Hahaha this made my day. And if OP reads this, you just ruined his. 

why thank you 

[Zodiark1593]

46 minutes ago, Froody129 said:

Although this is a very simple problem, I always break it up into powers of 10.

 

So in 40 we have 4 10's. What's 15% of 10? Easy, 1.5. 1.5x4=6.

So your brain operates on the RISC principle. 

 

I did something similar myself. 10% of 40 is 4. 5% is 2. Adding those gives me 6, which is 15% of 40.

 

There are more definitive and versatile means to go about this, but with this particular number, the above was quickest for myself. My math professors hated me for abusing such shortcuts whenever I could. 

[Froody129]

19 minutes ago, Zodiark1593 said:

So your brain operates on the RISC principle. 

 

I did something similar myself. 10% of 40 is 4. 5% is 2. Adding those gives me 6, which is 15% of 40.

 

There are more definitive and versatile means to go about this, but with this particular number, the above was quickest for myself. My math professors hated me for abusing such shortcuts whenever I could. 

RISC principle? Googled it and it seemed to just be optimising for maximum speed. 

 

 

Agreed, math teachers aren't very impressed with my working out. Although I might take slightly longer to work it out than some abstract shortcut, I never have to bother memorising that random rule. 

[Totallycasual]

5 hours ago, echy said:

what is 15 % of 40?

walk me step by step?

Some of our brains are just wired a little differently, the way i worked that out was to think ok whats 10% of 40? I just moved the decimal point over once, 4 is 10% of 40 that's easy enough so just half that to get the number for 5% which is 2 then add it onto the original 4, brings you to 6. 

 

I'm sure some people will say that its the ass about way to get there but trying to crunch numbers in my head literally hurts, it makes my brain feel like its stuttering or about to have a critical error and blue screen lol

[Zodiark1593]

46 minutes ago, Newenthusiast said:

Some of our brains are just wired a little differently, the way i worked that out was to think ok whats 10% of 40? I just moved the decimal point over once, 4 is 10% of 40 that's easy enough so just half that to get the number for 5% which is 2 then add it onto the original 4, brings you to 6. 

 

I'm sure some people will say that its the ass about way to get there but trying to crunch numbers in my head literally hurts, it makes my brain feel like its stuttering or about to have a critical error and blue screen lol

This brain doesn't seem to take well to serial problems such as math, and short term memory could be described as sketchy, but I find it quite easy to put through startling quantities of information through it when obsessively researching particular topics. It's long term memory is also very good. 

 

Back in elementary, I'd have several encyclopedias at once that I would flick through in turn. I did this far more often that I was doing school work and homework, much to the detriment of the latter. More recently, this has translated to rapidly inflating tab counts across multiple displays during obsessive research stints, and a quickly dying data cap that looms in the back of my mind. 

 

Once fixated upon a topic, I tend to lose many hours of sleep, researching until there is naught left for the internet to offer. 

Edited April 30, 2017 by Zodiark1593

[yathis]

7 hours ago, echy said:

what is 15 % of 40?

walk me step by step?

10% is 4

5% is half of 4

6

 

Calculator 40 x 0.15

Google does math for you