A sample of polystyrene is composed of a series of fractions of different-sized molecules:

FRACTION Weight fraction Moleculer weight
A 0.10 12,000
B 0.19 21,000
C 0.24 35,000
D 0.18 49,000
E 0.11 73,000
F 0.08 102,000
G 0.06 122,000
H 0.04 146,000

Calculate the number-average and weight-average molecular weights of this polymer sample.