How many glasses are in a magnum of champaigne?

You will get 6 glasses per bottle.

http://wiki.answers.com/Q/How_many_glasses_in_bottle_champagne

A magnum is 1.5 liters, which is about 50 oz. That's be enough for 10 5-oz glasses, or 12.5 4-oz glasses.

https://www.leaf.tv/articles/how-large-is-a-magnum-of-wine/

That last answer shouts out for my teacher's comment 'show your working'!
We are agreed that a magnum contains 1.5 litres.
The unknown is what is meant by 'a glass'. Wine glasses come in various sizes, most commonly from 4 to 10 fluid ounces. But special glasses called 'flutes' are sold for drinking champagne, and again these can be of various sizes.
http://www.cater4you.co.uk/plastic-champagne-glasses.htm
This site sells flutes in sizes from 100 ml to 255 ml.
Using the smallest would give you 15 'glasses', while the latter would give just under 6 'glasses'.

Taking this premise further, you can actually buy a champagne flute as small as 75ml. This would further extend the amount of glasses per magnum!

Would 75ml be the smallest champagne flute available? It's certainly the smallest capacity glass I've encountered.

I found the tiny 75ml glasses here: http://www.eventsupplies.co.uk/product_listing,6,166,Plastic_Champagne_Flutes.html