In a school,the following codes were used during physical exercise. $1$ means 'start walking',$2$ means 'keep standing',$3$ means 'start running at the same spot',$4$ means 'sit down'. How many times will a student who performs the following sequence without error from the beginning to the end have to sit down?
$1, 2, 3, 4, 2, 3, 1, 4, 4, 3, 2, 2, 1, 2, 4, 3, 1, 4, 4, 1, 2$

How many $8$'s are there in the following number series which are exactly divisible by their immediately preceding and also divisible by their immediately succeeding numbers?
$8, 2, 4, 5, 1, 7, 2, 8, 4, 8, 4, 2, 2, 8, 2, 6, 9, 8, 4, 5, 4, 8, 3, 2, 8, 4, 3, 1, 8, 3$

There are $20$ people working in an office. The first group of $5$ works between $8:00 \,A.M.$ and $2:00 \,P.M.$ The second group of $10$ works between $10:00 \,A.M.$ and $4:00 \,P.M.$ And the third group of $5$ works between $12$ noon and $6:00 \,P.M.$ There are $3$ computers in the office which all the employees frequently use. During which of the following hours are the computers likely to be used most?

How many $3$'s are there in the following sequence which are neither preceded by $6$ nor immediately followed by $9$?
$9, 3, 6, 6, 3, 9, 5, 9, 3, 7, 8, 9, 1, 3, 9, 6, 3, 9$

In the following series of numbers,find out how many times $1, 3$ and $7$ have appeared together,with $7$ being in the middle and $1$ and $3$ on either side of $7$?
$2, 9, 7, 3, 1, 7, 3, 7, 7, 1, 3, 3, 1, 7, 3, 8, 5, 7, 1, 3, 7, 7, 1, 7, 3, 9, 0, 6$

How many $6$s are there in the following number sequence which are immediately preceded by $9$ but not immediately followed by $4$? $5, 6, 4, 3, 2, 9, 6, 3, 1, 6, 4, 9, 6, 4, 2, 1, 5, 9, 6, 7, 2, 1, 4, 7, 4, 9, 6, 4, 2$