1)1/24         2)5/108        3)1/54          4)7/216

2)A coin is tossed 3 times. The probability of getting head and tail alternately is?

1)1/6           2)1/8            3)1/4         4)1/3

3)Three dice are thrown simultaneously. The probability of obtaining a multiple of 5?

1)1/36         2)5/108        3)1/54          4)43/216

Answer：

1）

6=1+1+4，3 possible outcomes
6=1+2+3，6possible outcomes
6=2+2+2，1possible outcomes
(3+6+1)/6*6*6=10/216 = 5/108

2）Here are the possible outcomes:
HHH, HHT, HTH, HTT, TTT, TTH, THT, THH
There are two outcomes that satisfy the alternate condition HTH and THT. Head and tail come alternatively in these two outcomes,
Total possibilities=8
Number of requirea outcome=2
Probability=2/8=1/4
So number 3) is correct answer

3/）

Maximum of three dice and 18
So that may occur in multiples of 5 to 5,10,15
As and when the 5: 5 = 1 +1 +3 will make arrangement with three kinds of 113
5 = 1 + 2 + 2 will be ordered to do 122 with three kinds of
And the time when 10 of 10 = 1 +3 +6 ordered to do 136 with 6
10 = 1 +4 +5 ordered to do 145 with 6
10 = 2 +2 +6 there are three kinds of ordered to do 226
10 = 2 +3 +5 ordered to do 235 with 6
10 = 2 +4 +4 there are three kinds of ordered to do 244
10 = 3 +3 +4 there are three kinds of ordered to do 334
When and when 15 = 3 +6 +6 15 366 do have three kinds of arrangement
15 = 4 +5 +6 ordered to do 456 with 6
15 = 5 +5 +5 555 ordered to do only one
In summary there and in multiples of 5 3 +3 +3 +6 +6 +6 +6 +3 +3 +3 +1 = 43
The vote occurred a total of three dice combination of a 6 * 6 * 6 = 216
The probability is 43/216 = 43/216

right or wrong?