✔ 最佳答案
For 15 rounds of games they played,
If Tim win 7 games, the marks he will get
= 7x4+(15-7)x(-1)
= 28-8
=20
If Tim win 8 games, the marks he will get
= 8x4+(15-8)x(-1)
= 32-7
=25
If Tim win 9 games, the marks he will get
= 9x4+(15-9)x(-1)
= 36-6
=30
If the score of Tim was less than 30 marks, max. no. of rounds that Tim can won is 8. Therefore,
the least number of rounds that Jack won
= 15-8
=7 nos. of rounds
If the question becomes ".... If the score of Tim was less than or equal to 30 marks ....", the least number of rounds that Jack won = 15-9 =6 nos. of rounds.
參考: my math. knowledge