Math Question

[Nikki]

I had my first Algebra class today and this was our first question:

How many 9's are there between 1 and 100?

I said 11. 9, 19, 29, 39......etc


Some students said 10, some said 11, some said 12.

During class, we kept going back to it and NOBODY could get the right answer. Right before we left, my instructor told us the answer. Nobody could figure out HOW she got that answer.

My friend just told me though. :

So, what is the answer?

 

[Vic C.]

Trick question... the answer is.......... 1!

:-D

 

[stray bullet]

I had my first Algebra class today and this was our first question:

How many 9's are there between 1 and 100?

I said 11. 9, 19, 29, 39......etc


Some students said 10, some said 11, some said 12.

During class, we kept going back to it and NOBODY could get the right answer. Right before we left, my instructor told us the answer. Nobody could figure out HOW she got that answer.

My friend just told me though. :

So, what is the answer?

There are literally no 9's between 1 and 100 when reading the phrase.
There is just one number 9 when counting whole numbers between the number 1 and the number 100.
There is also 19 9s-> 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 and 99 when counting whole numbers.

There's also an infinite amount of 9s if counting all possible non-whole numbers beteen 1 and 100. That is, 1.9, 1.99, 1.999, 1.9999, etc

 

[cubedbee]

There is also 19 9s-> 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 and 99 when counting whole numbers.

I'm pretty sure this is the answer they were looking for, and while you're correct that these 19 numbers are the only one containing 9s, there are actually 20 9s total, since 99 has two of them.

 

[stray bullet]

There is also 19 9s-> 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 and 99 when counting whole numbers.

I'm pretty sure this is the answer they were looking for, and while you're correct that these 19 numbers are the only one containing 9s, there are actually 20 9s total, since 99 has two of them.

Well, I was counting the number of whole numbers with them, not the actual numbers of 9s in that, so you're quite correct in that regard.

 

[Nikki]

There is also 19 9s-> 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 and 99 when counting whole numbers.

I'm pretty sure this is the answer they were looking for, and while you're correct that these 19 numbers are the only one containing 9s, there are actually 20 9s total, since 99 has two of them.

And YOU are correct. :D

In class, most said 10 or 11. We were all counting by 10's and forgot 90, 91, 92, 93.......

Then we said "One" because there is only one single 9.

You have the correct answer though!

 

[Nikki]

Trick question... the answer is.......... 1!

:-D

Wrong.

:

That's one of the answers that I gave, but she said no. As we were leaving class, she said the answer was 20. We still couldn't figure out how though. I guess we were all saying in our minds "9, 19, 29, 39.....99". We kept forgetting "90, 91, 92, 93, 94.... and then the two 9's in 99".

:

 

[Quath]

That is a badly worded question. My answer would have been infinity.

1.9, 1.99, 1.999, 1.9999, ........9.99999999999999 etc.

A slightly better question would have been

"How many times does the digit '9' come up in the counting numbers between 1 and 100?"

Quath

 

[Nikki]

That is a badly worded question. My answer would have been infinity.

1.9, 1.99, 1.999, 1.9999, ........9.99999999999999 etc.

A slightly better question would have been

"How many times does the digit '9' come up in the counting numbers between 1 and 100?"

Quath

That's the kind of stuff my class was saying. None of us could figure out how she got 20.

 

[stray bullet]

It is easy.

100 has no 9s in it, so we need to only evaluate numbers 1-99.

All numbers with 9 in it will look like
x9 or 9x, where x is 0-9. So that's 10 numbers that end with 9 and 10 numbers that begin in 9.

 

[Cedric]

That is a badly worded question. My answer would have been infinity.

1.9, 1.99, 1.999, 1.9999, ........9.99999999999999 etc.

A slightly better question would have been

"How many times does the digit '9' come up in the counting numbers between 1 and 100?"

Quath

I think you mean natural numbers. 8-)

 

[cubedbee]

That is a badly worded question. My answer would have been infinity.

1.9, 1.99, 1.999, 1.9999, ........9.99999999999999 etc.

A slightly better question would have been

"How many times does the digit '9' come up in the counting numbers between 1 and 100?"

Quath

I think you mean natural numbers. 8-)

I think you both mean positive integers.
;-)
http://mathworld.wolfram.com/WholeNumber.html

 

[Quath]

That is a badly worded question. My answer would have been infinity.

1.9, 1.99, 1.999, 1.9999, ........9.99999999999999 etc.

A slightly better question would have been

"How many times does the digit '9' come up in the counting numbers between 1 and 100?"

Quath

I think you mean natural numbers. 8-)

I think you both mean positive integers.
;-)
http://mathworld.wolfram.com/WholeNumber.html

I have been pedagogically outdone. :P

Quath

 

[cubedbee]

I just read this question in a puzzle book, but it was phrased "There are 100 buildings along a street. A signmaker is ordered to number the buildings from 1 to 100. How many 9's will he need." Very clever---this way it's unambiguous what answer you're looking for.

 

[IVA]

lol i quit math.... back 3 years ago or something like that.... soooo I prolly wouldent have figured that out if my life depended on it!!!