Why can't i use the "direct" way to get correct answer?

[aimhier]

Manhattan GMAT Challenge Problem of the Week - 13 Feb 2012

Each of three investments has a 20% of becoming worthless within a year of purchase, independently of what happens to the other two investments. If Simone invests an equal sum in each of these three investments on January 1, the approximate chance that by the end of the year, she loses no more than 1/3 of her original investment is

A. 90%
B. 80%
C. 70%
D. 60%
E. 40%
Why can't i use the "direct" method to get the correct answer A? no more than 1/3rd" being lost means that she got all three win:(0.8)(0.8)(0.8) = 0.064, or exactly 1 loss : (0.2)(0.8)(0.8) = 0.128 they don't add up to 90% ; WHY?

[jnelson0612]

Hi,
I just answered this one on the other forum. :-)