Half challenge. 
( Half ( challenge . ) )
(ROOT (S (NP (NN Half)) (VP (VBP challenge)) (. .)))
One part challenge, one part adventure.
( ( ( ( One ( part challenge ) ) , ) ( one ( part adventure ) ) ) . )
(ROOT (NP (NP (CD One) (NN part) (NN challenge)) (, ,) (NP (CD one) (NN part) (NN adventure)) (. .)))