Question

it is possible to replace resistors joined in series by an equivalent single resistor of resistance. How?

Answer 1

yes by calculating the resistance in series we can replace it with a resistor whose value is same as equivalent resistor.......

Answer 2

Yes, It's possible to replace resistors joined in series by an equivalent single resistor of resistance.
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Let us consider three resistors R1 ,R2 and R3 connected in series.
Let R1=1ohms.
R2=2ohms
R3= 3ohms
Now when resistors are connected in series same current flows .
IAB=I1=I2=I3.
Equivalent resistance Req=R1+R2+R3
= 1ohm + 2ohm+3ohm
=6ohms.
Now resistors in circuit can be replaced by equivalent single resistor of 6ohms