Chapter 9.1, Problem 23ES

Suppose $A\left[1\right],A\left[2\right],A\left[3\right],\mathrm{....},A\left[n\right]$ is a one-dimensional array and $n>50.$
a. How many elements are in the array?
b. How many elements are in the subarray $A\left[4\right],A\left[5\right],\mathrm{...}A\left[39\right]?$
c. If $3\le m\le n,$ what is the probability that a randomly chosen array element is in the subarray $A\left[3\right],A\left[4\right],\mathrm{....},A\left[m\right]?$
d. What is the probability that a randomly chosen array element is in the subarray shown below if $n=39?$
   $A\left[\lfloor n/2\rfloor \right],A\left[\lfloor n/2\rfloor +1\right],\mathrm{....},A\left[n\right]$