Question

how to solve Rtot from 1/R+1/3R=1/Rtot

Answer 1

Which grade do you study in ?

Answer 2

6

Answer 3

So you have not been taught to add fractions ?

Answer 4

No not yet...

Answer 5

I want to learn new things

Answer 6

Its simple; to add \[\frac{ a }{b }+\frac{ c }{ d }\]
first make their denominator same.

This can be done by finding LCM (Least Common Multiple) of the denominators (namely b and d)
Or you can simply make each denominator equal to the product of the two denominators (i.e. b*d)

Here, I will use the second approach.

A fraction remains same when it is multiplied and divided by the same number; so
\[\frac{ a }{b }+\frac{ c }{ d }=\frac{ a*d }{ b*d }+\frac{ c*b }{ d*b }\]

When the denominators are same, you can add the (new) numerators like integers. So
\[\frac{ a }{b }+\frac{ c }{ d }=\frac{ a*d+c*b }{ b*d }\]

As an exercise - solve
\[\frac{ 1 }{ R }+\frac{ 1 }{ 3R }\]

Answer 7

@AlexKrakoq
You wanted to learn how to do the calculation or just the answer ??