Question 69687
My child has a maths question in Foundation of Mathematics by A J Sadler and the answer in the book = 50. I do not get that answer but my child can using calculator equations. My child needs to understand the method and I do not know where I'm going wrong. I can normally work these problem out but I need help with this one:

1/R = 1/R1 + 1/R2 + 1/R3 where R = 20, R2 = 40 and R3 = 200

1/20 = 1/R1 + 1/40 + 1/200
The LCD is 200R1, multiply everything by 200 to clear the fractions.
{{{200R[1](1/20)=200R[1](1/R[1])+200R[1](1/40)+200R[1](1/200)}}}
{{{10R[1]=200+5R[1]+R[1]}}}
{{{10R[1]=200+6R[1]}}}
{{{10R[1]-6R[1]=200+6R[1]-6R[1]}}}
{{{4R[1]=200}}}
{{{4R[1]/4=200/4}}}
{{{highlight(R[1]=50)}}}
Happy Calculating!!!!