Solution:

The first two digits are fixed.
You are left with eight digits (since one digit can be used just once).
Also you have only 4 more digits left to frame a phone number.

Thus the possibilities = 8P4 = 1680.

Solution:

Since she has to distribute the chocolates in a manner that none of her friends receive less than 10 chocolates, it is clear that everyone will get at least 10 chocolates which means that 50 chocolates will be distributes offering 10 to each.

Now only 6 chocolates are remaining which has to be distributed among 5 persons

It can be possible in

6+5-1C5-1 = 10C4 = 10C6

Thus option a is correct.

Solution:

1000

Explanation:
Total number of methods selecting three question out of five in one section = 5*4/2*1 = 10
Since there are three sections and selection has to be made in each of them
Total methods = 10*10*10 = 1000

Solution:

160600