Shrimp Colony Q?

Hormones.

LOL... of course. But would it really happen. Would 10 eventually 10 to 20 to 40 to 80 to 120, etc?

Ten is more than enough i started with ten yellows in a 56 gal now have over 40 maybe more in about 2 months

10-20 is a fine number to start off with. They will breed quite readily, especially if you start off with easier shrimp like RCS.

20 shrimp + patience + clean water + plenty of food = a colony in no time

Depends on how big and how fast do you want the colony to grow. The more adults shrimp in the tank, the faster the number of shrimp you will have in there will grow. Ten sounds like a good start, or 20 in a ten gallon would be even better, especially if you are not as patient (like me) and want to see a huge colony quicker.

Each female will carry about 15-40 eggs. Figure 50%-75% will survive.
Be careful with your water changes.
All you need is one berried female and you've got an instant colony.
-Gordon

I was an impatient one: got 20 from one source, then got another 20 from a different source, 2 weeks later got another 20. I've traded, sold, acquired, and now I just had 10 females hatch her babies...

8 shrimp + clean water + free food = 1000+ shrimp in 2 years

your results may vary