## Your Questions About Odd Calculator

David asks…

## serial numbers scratched out on graphing calculator?

I apologize for my ignorant question. Please don’t be mean, haha!

I just bought a secondhand TI-83 **calculator** off someone in my city (listed online). I only paid $20 and it works great. I just noticed, however, that most of the serial numbers on the back have been scratched out. i.e. only 5 numbers are intact.

Does this mean that the person I bought it from had stolen it off of someone?? Or did she buy it from a pawn shop (i.e. it was pawned as a stolen good)? She lives in a low-income area of town so I wouldn’t doubt this.

Sorry for my stupidity…but what impact does this have on me? i.e. do I possess stolen property? Might there be something wrong with the **calculator** itself? Anyone have a similar experience?

Any good input please, thanks.

The numbers are definitely deliberately scratched off. Yeah, haha I know, those Texas Instruments calculators are pretty much indestructable.

### admin answers:

It’s possible, but very unlikely, that someone got bored one day and scratched the number off. The odds, however, are that the calculator was stolen. There’s not much you can really do about it at this point. If you had noticed it before you purchased it, you could have turned it done. If you really feel you want out of it, talk to the police department. You didn’t knowingly buy a stolen article and you’re trying to make it good, so they have no reason to do anything to you. If it was reported, they can see of the serial numbers that remain are in their files. You could just toss it, $20 isn’t that big a deal. Or you could give it to Good Will or something like that. Other than that, use it and just learn from the experience.

Paul asks…

## Please can you work out my odds?

Have a football bett 4 games £10 bet in total

all of the games are for the home team to win the odds are

2/5 home win

8/13 home win

1/8 home win

4/9 home win

What will my return be with the £10 total stake

Thanks

### admin answers:

Your bet will return approx £36.73

There is a bet calculator available on my website

See below.

George asks…

## Help with odds please?

ok a game board contains 80 numbers

20 numbers are drawn

9 numbers of the 80 are mine.

what are the odds that i get

1,2,3,4,5,6,7,8,9 of those numbers?

oh yes forgot to say thank you

also if u could include how many draws or games it would take to get each of these for instance

1 in 58746 to get all 9 numbers

1 in 47654 to get 8 out of the 9 etc etc.

please help =)

### admin answers:

The number of ways you can draw 20 from 80 is 80C20. Now if we assume that n of the 20 numbers are yours then the other 20-n numbers are drawn randomly from 80-9 since they have to be drawn from the 71 numbers that are not yours. This leaves 71C(20-n) ways to draw the last 20-n numbers. The number of ways that you can have n of your 9 numbers are 9Cn. This reasoning provides the formula:

your odds = 9Cn*71C(20-n) to 80C20

Where n denotes an amount between 1 and 9 of how many numbers you got right.

17 in 23,471,690 to get all 9 which is approximately

1 in 1,380,688

153 in 4,694,338 to get 8 which is approximately

1 in 30,682

But you have the formula so just calculate 9Cn*71C(20-n) in 80C20 and let your calculator reduce the fraction between the two in order to get these relations.

It has to be said, that these numbers really show what the tendency is on THE LONG RUN. But there is another concept called the „mean waiting time“ which denotes the theoretic mean of the number of draws before you succeed.

This is a somewhat lower number than the numbers above because an instance of probability 1/n usually happens before n trials has been carried out.

To see this consider a dice. It will usually show six before six repetitions. So the mean waiting time for the occurence of a six is lower than 6 though the probability is 1/6.

Ken asks…

## Graphing calculator for Algebra 2?

Hi, I’ve started up my junior year, and my algebra 2 teacher said that a graphing **calculator** was highly reccomended. I tell my mom this, and the next day I find a bag on my desk. However, I saw that this **calculator** was over $100, and I put myself on a massive guilt trip, because to be honest I don’t know if I really NEED this **calculator** or how much easier it’ll make my class.

Thanks a lot for the speedy responses!

As I don’t have much love for math, I think I’ll keep it and consider it an investment for other courses. Glad to hear it’ll save me some writing.

Thanks again!

### admin answers:

Trust me you really need the calculator, and for SATs and college and every math course from now until you’re done with school for good. Dont worry about it! 😛

those calculators are so helpful. That’s odd that your school doesnt lend them to you, that’s what mine does. So now i have the dilemma of not having my own for college yet D:

you’re a lucky one! Haha

Robert asks…

## easy math i just dont have a scientific calculator?

Question 1:

3 + 2 =

Question 2:

3 + (- 2)=

Question 3:

6 + (+ 7) =

Question 4:

(- 4) + (- 5) =

Question 5:

(+ 12) + (- 12) =

Question 6:

(- 8) + (+ 8) =

Question 7:

(- 7) + (+ 4) =

Question 8:

(+ 7) + (- 4) =

Question 9:

(+ 5) + (- 8) =

Question 10:

(+ 6) + (+ 5) =

Question 11:

(- 6) + (- 5) =

Question 12:

(- 3) + (+ 3) =

Question 13:

(+ 2) + (- 12) =

Question 14:

(-{- 7) + (- 6) =

Question 15:

(-6)+(-9) =

Question 16:

(- 3) + (- 12) =

Question 17:

(- 7) + (+15) =

Question 18:

(- 1) + (+ 8) =

Question 19:

(+ 3) + (- 7) =

Question 20:

(-4) – (-8) =

### admin answers:

If you managed to type this into Y!A and have an account here, chances are very good that you have a scientific calculator. If you are running some flavor of MS Windows, In NT, 2000, and XT, you can get to it by going to Start -> All Programs -> Accessories -> Calculator. By default you get just a four-banger, but if you go into the View menu, you can select the scientific calculator instead. The procedure for getting to the calculator will be a bit different for MAC machines, but they have one also.

Meanwhile, except for the signs, this is just mental arithmetic.

Rules for signed addition/subtraction:

1. Convert subtracts to adds by changing the sign of the subtrahend (the number you are subtracting). Then use the rules for addition. Taking #20 as an example,

-4 − (-8) = -4 + (+8)

or you may prefer to think of it as

-4 + (-(-8)) and use rule 2 below to clear out the redundant negative signs.

2. For numbers with nested multiple negative signs in front of them, such as #14, the negative signs will obey the same rules as for multiplication and division: count the negative signs and negative signs cancel in pairs. If the number of negative signs is even, they all canceled and the result is positive. If the number is odd, there is one negative sign left after cancellation is complete and the result is negative.

Example: -(-7) = 7 because two is even and all the negative signs cancelled.

-(-(-(-(-7) = -7 because 5 is an odd number and like signs, so one is left over at the end.

3.

A. To add numbers of LIKE SIGN, add the absolute values (magnitudes) of the numbers to get the magnitude of the answer. The sign will be the same as the sign of the numbers.

B. To add numbers of OPPOSITE SIGN, subtract the magnitudes (absolute values) of the numbers to get the magnitude of the answer. The sign will be the same as that for the number with the larger magnitude. If both numbers have the same magnitude, as in questions 5 and 6, the answer will be zero, which has no sign.

Using example #20 again:

(-4) + (+8) (or, if you prefer, -4 + 8)

Unlike signs, so subtract the magnitudes 8 and 4 to get 4. The number with the larger magnitude is 8, which is positive, so the answer is +4. In signed arithmetic, numbers are typically assumed to be positive unless otherwise specified, so you may drop the redundant + sign, as is conventionally done.

Now do the others, preferably without a calculator. You really need to master signed because it will continue to haunt you in your math and science courses until you do.

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