# Parallel circuit-find value of resistor [closed]

I have a parallel circuit with 7.5 ohms as total resistance,75 volts, with 2 resistors. R1=10ohms,R2 is unknown. How can I find the value of R2?

• Show your circuit and your work. – DerStrom8 Feb 19 '17 at 0:57
• I'm voting to close this question as off-topic because it appears to be a homework question with no prior attempts shown, and the OP couldn't even be bothered to provide a schematic. – DerStrom8 Feb 19 '17 at 0:58

Since $R_{tot}=\frac{R_1\cdot R_2}{R_1+R_2}$ it follows from simple algebra that $R_2=\frac{R_1\cdot R_{tot}}{R_1- R_{tot}}$. In this case, that means $R_2=\frac{10\:\Omega\cdot 7.5\:\Omega}{10\:\Omega- 7.5\:\Omega}=30\:\Omega$. The voltage you mentioned isn't required.