How many 18 Q resistors must be connected in series to give

How many 18 Q resistors must be connected in series to give an equivalent resistance to five 630 Ohm resistors connected in parallel?

Solution

5 resistors of 630 ohms in parallell means 1/R = 1/630 + 1/630 ......( 5 times )

1/R = 5/630

R = 126 ohms

So no of 18 ohm resistors to be connected in parallel is 126/18 = 7 resistors

So answer is 7