if we assume there is a 50-50% chance of having a girl or a boy then:

so what is the chance that you have a girl first?

50%, what is the chance you have a girl again? 50% and so on

so:

1 boy 50% chance
1 boy + 1 girl 25% chance
1 boy + 2 girl 12.5% chance
1 boy + 3 girl 6.25% chance
etc
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Number of boys is:
SUM as n goes from 1 to infinity of (0.5^n)
Number of girls is:
SUM as n goes from 1 to infinity of ((n-1)*0.5^(n+1))

so the ratio is the ratio of those two values.