If you double something four times, which you would do over a thirty-year period if you did that every 7.6 years, you would wind up with sixteen times the original amount. Two to the fourth power. 2-4-8-16. Or...1600 percent.

 

And the purchase price of a bond is...uhhhhh...what you originally paid for it...which cannot change, except, perhaps, with the assistance of a time machine. 

 

Idiot.