My Arthmetic Sequence

My sequence : $5,10,15,20, 25$ …

how to find $t_{50}$ : $t_{50}$ = 5 + (50 – 1) (5)

$t_{50}$ = 5 + 245

$t_{50}$ = 250

$t_n$ = $t_1$ + (n – 1)(d)

$t_n$ = 5 + (n – 1)(5)

$t_n$ = 5 + ( 5n – 5)

$t_n$ = 5n

$S_{50}$ = $\frac {50}{2}$ ((2)5 +(25 – 1)(5))

$S_{50}$ = 25 (130)

$S_{50}$ = 3250

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