Question 1:   The initial term of an arithmetic progression is  $a_1=3$  and difference  $d=0.3$ .  Find  $a_{11}$ .

Question 2:   Arithmetic progression is given by formula  $a_n=10-n$  .  Find  $a_4$ .

Question 3:   Find the difference  $d$  of an arithmetic series if  $a_1=6,a_8=-50$ .

Question 4:   Find the initial term of an arithmetic series  $\left(a_n\right)$ ,  if  $a_{15}=20$  and the common difference  $d=0.5$ .

Question 5:   Find the formula of the nth term of an arithmetic series  $\left(a_n\right)$ :  $-3,-5,-7,-9\mathrm{...}$  (-3 is the initial term).