Solution:

"Bodo weighs 90 pounds" is the correct answer. His sister weighs 30 pounds. Thus, Bodo weighs 60 pounds more than his sister and their combined weight is 120 as per the problem requirements.

The common mistake is to quickly jump to the conclusion that "Bodo weighs 60 pounds and his sister weighs 60 pounds." But, Bodo would then erroneously weigh 0 pounds more than his sister.

Alternative Solution through Equations:

Let b be Bodo's weight and s be his sister's weight. Then,

b − s = 60; and
b + s = 120.

On solving the above two equations, we get

b = (60 + 120) / 2 = 90.