1: my own arithmetic sequence: 20，22，24，26，28，30

first five numbers: 20, 22, 24, 26, 28,30

2: , d=2

20+49×2=t_{50}=118

3: $latex t_{1}+(n-1)d=t_{n}

=20+(n-1)2

=20+2n-2

=18+2n

4:(sorry Ms Burton, I don’t know how to type the formula, but I post the process oƒ calculating the sum of the 50 terms)