The average number of playing cards Oscar and Charlie had was 458. The average number of playing cards Oscar and Neave had was 220. If the ratio of Charlie's playing cards to Neave's playing cards was 9 : 2, find the number of playing cards Oscar had.
Total number of cards that Oscar and Charlie had
= 2 x 458
= 916

Total number of cards that Oscar and Neave had
= 2 x 220
= 440

Number of playing cards Charlie had = 9 u
Number of playing cards Neave had = 2 u

Oscar's cards + 9 u = 916 --- (1)
Oscar's cards + 2 u = 440 --- (2)

(1) - (2)
9 u - 2 u = 916 - 440
7 u = 476
1 u = 476 ÷ 7 = 68

Number of playing cards that Neave had
= 2 u
= 2 x 68
= 136

Number of playing cards that Oscar had
= 440 - 136
= 304

Answer(s): 304