How are resistor connected in series?

when we want maximum resistance they are connected in series.

when resistors are connected in series total resistance is maximum

when resistors are connected in parallel total resistance is minimum

for series total R=R1+R2+R3.........

for parallel R1 in parallel to R2 total 1/R=(1/R1)+(1/R2) ie R=(R1*R2)/(R1+R2)