2 resistors of resistances 150 ohms and 5000 ohms respectively are in series with each other. They both are also in parallel with a 1000 ohm resistor. What is the total resistance?
Firstly, you should start by working out the total resistance for the 150 ohm and 5000 ohm resistors which are in series: -In series the total resistance is given as the sum of the resistance of each individual resistor (RT=R1+R2+R3...). -Therefore the total resistance of the 150 ohm and 5000 ohm resistors is 5150 ohms (150+5000=5150) Imagine this total resistance of the resisitors in series (5150 ohms) being a resistor that replaces both the 150 ohm and 5000 ohm resistors. Now try working out the total resistance in parallel: -In parallel the reciprocal of the total resistance is given as the sum of the reciprocal of resistance for each individual resistor (1/RT = 1/R1 + 1/R2 + 1/R3 ...) -Therefore the reciprocal of the total resistance is 1/5150 + 1/1000 = 123/103000. So to obtain the total resistance divide 1 by this value (as it is a reciprocal) to get a resitance of 103000/123 ohms which is equivalent to 837.4 ohms (4 s.f.)
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