f.3 questions 20marks

[匿名]

2011-01-03 1:44 am

1 . The athletic team of a school has m boys and n girls.
The mean time taken to finish a 400m race for the whole team is 70 seconds.

a) If the mean time taken for the boys is 62 seconds and that for the girls is 75 seconds , find the ratio m : n .

b) If there are 39 members is the team, find the number of boys.

2 . 9 square tiles of side 20 cm are placed as shown in the figure.
A coin of radius 1 cm is thrown at random to the table. It is known that the coin falls on to the tiles.

圖片參考：http://imgcld.yimg.com/8/n/HA06878030/o/701101020099913873435450.jpg

a) Find the area of the region in which the centre of the coin may lie.
b) Find the probability that the coin does not fall onto any edge of a tile.

回答 (1)

用戶2053

2011-01-03 2:41 am

✔ 最佳答案

1a)
62m + 75n = 70(m + n)
75n - 70n = 70m - 62m
5n = 8m
m : n = 5 : 8b)
Number of boys = 39 x (5/(5+8)) = 15
2a)
(20 x 3 - 1 - 1)² = 58² = 3364 cm²b)
(20 - 1 - 1)² x 9 / 3364
= 729/841

2011-01-02 18:50:23 補充：
If the coin can be outside the tiles partial:

2a)
(20 x 3 + 1 + 1)² = 62² = 3844 cm²

b)
(20 - 1 - 1)² x 9 / 3844
= 729/961

👍 0 👎 0