1. If 4^x+2 - 4 ^x+1 = 48
x=?
2. The probabilities for A and B to solve a problem are 1/5 and 3/5 respectively.
3. If A and B work indipendently, the probability that the problem is solved is?
The mean of six numbers 3, 3, 5, 5, 15, z is 6. What is the mode ?
urgent !!
2007-03-31 8:07 pm
回答 (3)
2007-03-31 9:04 pm
✔ 最佳答案
揀我做最佳啦^^ 因為樓上做錯左第2題，又冇答到第3題 (第3題唔係問z，係問mode)。
圖片參考：http://i169.photobucket.com/albums/u209/lautszki/07-3-30/P.jpg
2007-03-31 11:58 pm
A1)
4^(x+2) - 4^(x+1) = 48
4^x .4^2 - 4^x . 4 = 48
16 . 4^x - 4 . 4^x = 48
12 . 4^x =48
4^x = 4
x = 1
A2)
P(problem is solved)
= 1 - P(A cannot solve it AND B cannot solve it)
= 1 - P(A cannot solve it ) x P(B cannot solve it)
= 1- (1-1/5) x (1 - 3/5)
= 1- 4/5 x 2/5
= 1- 8/25
= 17/25
A3)
We find z first,
6 x 6 = 3+3+5+5+15+z
z = 5
Mode = The most appeared number
= 5 (因為5總共出現了3次,是眾數中出現次數最多的)
4^(x+2) - 4^(x+1) = 48
4^x .4^2 - 4^x . 4 = 48
16 . 4^x - 4 . 4^x = 48
12 . 4^x =48
4^x = 4
x = 1
A2)
P(problem is solved)
= 1 - P(A cannot solve it AND B cannot solve it)
= 1 - P(A cannot solve it ) x P(B cannot solve it)
= 1- (1-1/5) x (1 - 3/5)
= 1- 4/5 x 2/5
= 1- 8/25
= 17/25
A3)
We find z first,
6 x 6 = 3+3+5+5+15+z
z = 5
Mode = The most appeared number
= 5 (因為5總共出現了3次,是眾數中出現次數最多的)
2007-03-31 8:39 pm
1) 4^x+2 - 4 ^x+1 = 48
(4^2)(4^x) - (4)(4^x) = 48
(16-4)(4^x) = 48
4^x = 4
X = 1
2) (1/5)(3/5) = 3/25
3) (3 + 3 + 5 + 5 + 15 + z) / 6 = 6
z = 36 - 3 - 3 - 5 - 5 - 15 = 5
(4^2)(4^x) - (4)(4^x) = 48
(16-4)(4^x) = 48
4^x = 4
X = 1
2) (1/5)(3/5) = 3/25
3) (3 + 3 + 5 + 5 + 15 + z) / 6 = 6
z = 36 - 3 - 3 - 5 - 5 - 15 = 5
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