簡單數學問題簡單數學問題

Tieria

2010-03-05 7:18 pm

1.Consider a group of number: 3, 4 ,5, 8, x. If the mean and the mode are the same, then x =
The answer is 5.

2. A fair dice is thrown three times. Find the probability that at least two ‘multiple of 3’ occur.
The answer is 7/27.

3. If point A is reflected along the line y = -4, the image obtained is (4, -2), find the coordinates of A.
The answer is (4, -6).

4. If log3 = a and log4 = b, then log18 =
the answer is 2a + b / 2.

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回答 (1)

用戶2053

2010-03-05 8:32 pm

✔ 最佳答案

1)The most must be x , so the mean also = x ,
(3 + 4 + 5 + 8 + x) / 5 = x
x = 5
2)P(multiple of 3’ occur) = P(3 or 6 occur) = 2/6 = 1/3
P(at least two ‘multiple of 3’ occur)
= P( two ‘multiple of 3’ occur) + P(three multiple of 3’ occur)
= 3*(2/3)(1/3)(1/3) + (1/3)^3
= 7/27
3)Let point A be (x , y)
then (4 , - 4) is the mid point between A and (4 , - 2)
So ( (x + 4)/2 , (y - 2)/2 ) = (4 , - 4)
x = 4 and y = - 6
A is (4 , - 6)
4) log 18
= log (2 * 3^2)
= log 2 + log 3^2
= log 2 + 2log 3
= log 4^(1/2) + 2log 3
= (1/2) log 4 + 2 log 3
= b/2 + 2a
= 2a + b/2

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