問4條數學20點(中一程度)

有*者即是要例式

1,Consider the sequence 2, 4, 8, 16,...
Find the general term of the sequence.

*2,Jack is x years old.The age of his father is 4 times of his age,and the age of his mother is 3 times of his age.
If the age of Jack's sister is 2 less than 1/3 of his mother's age,express the age of his sister in terms of x.

*3,The running speeds of 4 athletes in a team are shown below:
Athlete A B C D
Running speed(m/min) 200 150 180 270
They join a 10 km relay marathon.
If the time taken for each of them is the same, find the percentage of the distance each of them runs.

4,The table below shows the eye colours of group of students in an international school.
Eye colour Brown Blue Black Green Hazel
Fraction of the total 1/4 x 1/5 1/20 1/10
Find the value of x.