Use the explicit formula a(n)=a(1) +(n-1)•d to find the 1000th term of the sequence- 24,31,38,45,52

24,31,38,45,52 is an Arithmetic Progression since the difference between one term and the preceding is CONSTANT:

31-24= 7

38-31 =7

45- 38 =7

In the explicit given formula [a(n)=a(1) +(n-1)•d],  a=24; d= 7 and n = 1000,
then the :

1000th term value = 24 + (1000-1).7 = 24 + (999).7 = 24 + 6993

1000th term value = 7017

Given:
9 members
elect 1 chairperson
elect 1 secretary
elect 1 treasurer

There are 9 choices for a chairperson.
There are 8 choices for a secretary. 
There are 7 choices for a treasurer.

9 * 8 * 7 = 504 Choice A.

There are 504 different slates of possible candidates