[abhorrence]

> a variable holding a 1 can turn into a "1" and back

This is true of Javascript, but not of Ruby.

  irb(main):001:)> 3 * "3"
  TypeError: String can't be coerced into Fixnum

People commonly conflate dynamic typing with weak typing, Ruby has the former, but not the latter (with some explicit exceptions, e.g. to_ary and friends).

That's not to say you can't still end up with some interesting problems though -- if we just slightly change your example:

  a = 3
  b = 3
  # later...
  a = "oops"
  product = a * b
  # product is now "oopsoopsoops"

But this isn't due to automatic "weak types" style coercion -- just that Ruby lets you build a repeated string by multiplying a string by a number.