# Newbie Question

**URL:** <https://www.ruby-forum.com/t/newbie-question/180674>\
**Category:** Ruby\
**Created:** [December 25, 2009, 5:12pm UTC](https://www.ruby-forum.com/t/newbie-question/180674 "2009-12-25T17:12:32Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![lalawawa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e480ec/32.png) [@lalawawa](https://www.ruby-forum.com/u/lalawawa)\
**Post date:** [December 25, 2009, 5:12pm UTC](https://www.ruby-forum.com/t/newbie-question/180674/1 "2009-12-25T17:12:32Z")

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How do I turn the string “4.5” into the number 4.5 so I can do  
arithmetic on it?

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**Author:** ![lalawawa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e480ec/32.png) [@lalawawa](https://www.ruby-forum.com/u/lalawawa)\
**Post date:** [December 25, 2009, 5:20pm UTC](https://www.ruby-forum.com/t/newbie-question/180674/2 "2009-12-25T17:20:49Z")

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lalawawa wrote:

> How do I turn the string “4.5” into the number 4.5 so I can do  
> arithmetic on it?

irb(main):017:0\> “4.5”.to\_f  
=\> 4.5

–  
Kind Regards,  
Rajinder Y.

[http://DevMentor.org](http://DevMentor.org)

Do Good! - Share Freely

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**Author:** ![lalawawa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e480ec/32.png) [@lalawawa](https://www.ruby-forum.com/u/lalawawa)\
**Post date:** [December 25, 2009, 5:34pm UTC](https://www.ruby-forum.com/t/newbie-question/180674/3 "2009-12-25T17:34:19Z")

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On Dec 25, 10:51 am, Rajinder Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> [http://DevMentor.org](http://DevMentor.org)
> 
> Do Good! - Share Freely

Thanks Rajinder, that did it!

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**Author:** ![lalawawa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e480ec/32.png) [@lalawawa](https://www.ruby-forum.com/u/lalawawa)\
**Post date:** [December 25, 2009, 6:04pm UTC](https://www.ruby-forum.com/t/newbie-question/180674/4 "2009-12-25T18:04:48Z")

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On Fri, Dec 25, 2009 at 3:51 PM, Rajinder Y. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> lalawawa wrote:
> 
> > How do I turn the string “4.5” into the number 4.5 so I can do  
> > arithmetic on it?
> 
> irb(main):017:0\> “4.5”.to\_f  
> =\> 4.5

Or if you want “4.5” to convert to a Float but “4.5q” to raise an  
error/exception:

Float(“4.5”) #=\> 4.5  
Float(“4.5q”) #=\> ArgumentError “invalid value for Float”