Two resistors are connected $(a)$ in series $(b)$ in parallel. The equivalent resistance in the two cases are $9$ $ohm$ and $2$ $ohm$ respectively. Then the resistances of the component resistors are
A$2$ $ohm$ and $7$ $ohm$
B$3$ $ohm$ and $6$ $ohm$
C$3$ $ohm$ and $9$ $ohm$
D$5$ $ohm$ and $4$ $ohm$
Medium
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B$3$ $ohm$ and $6$ $ohm$
b (b) ${R_1} + {R_2} = 9$ and $\frac{{{R_1}{R_2}}}{{{R_1} + {R_2}}} = 2$ $ \Rightarrow $ ${R_1}{R_2} = 18$
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