练习题 · 英文原题 · SEL-MA-TST-09
In Ms Petrakis's school choir there are 3 boys for every 5 girls, and 40 children altogether. Then 6 more boys join the choir.
How many more girls must join so that there are again 3 boys for every 5 girls?
查看答案与解析(英文)
答案: C
Answer: C (10)
- Each group of 3 boys and 5 girls has 8 children. 40 ÷ 8 = 5 groups, so there are 15 boys and 25 girls.
- After 6 boys join there are 15 + 6 = 21 boys, which is 21 ÷ 3 = 7 groups of 3 boys.
- 7 groups need 7 × 5 = 35 girls.
- More girls needed: 35 − 25 = 10.
Why the other options are wrong
- A (6): This adds the same number of girls as boys, but there must be 5 girls for every 3 boys, so more girls than boys must join.
- B (7): This is the number of groups of 3 boys, not the number of girls to add.
- D (35): This is how many girls the choir needs altogether, not how many more must join.
- E (56): This is the size of the whole choir after the new girls join (21 + 35), not the number of new girls.

