Question 25686
Formula: A=P(1/2)^(t/1234)
A is the amount you have after some years.
P is the amount you started with.
t is the number of years since the start time.
You want A=10%(p)= 0.1P
So, you have 0.1P=P(1/2)^(t/1234)
0.1=2^(-t/1234)
Take the ln of both sides to get:
 ln(0.1)= (-t/1234)(ln 2)
  t=[-1234{ln 0.1)/(ln 2)]
I don't have a calculator with me so I will leave
the calculating to you.

Cheers,
Stan H.