Average weight of 8 gold coins is 20 g per coin. Average weight of 12 silver coins is 35 g per coin. What is the average weight per coin for 20 coins?

29 g

Sum of weight of 8 gold coins = 8 × 20 = 160g

Sum of weight of 12 silver coins = 12 × 35 = 420g

Average weight of all 20 coins = \(\frac{420 + 160}{20}\)

= \(\frac{580}{20}\) = 29 g