Simple problem calculate total Resistance parallel

[late347]

Homework Statement

I made this problem on my own.
resistors are
10 ohms
30 ohms
15 ohms

they are in parallel connections between A and B points
Voltage across A and B = 12 volts
calculate R_total

Homework Equations

1/ R = 1/ R₁ ´+ 1/R₂ + 1/R₃

The Attempt at a Solution

1/R = 1/10 +1/30 + 1/15

1/R = 6/30 = 1/5

R/1 = 30/6 = 5/1
R= 5 ohms

If the inverse of R = 6/30

I guess then R itself should be inverse of (6/30) = 30/6

I think I got the same result with the laborious method.

1/R = 6/30 ]]]] * R
1= 6R/30 ]]]] * 30
30= 6R ]]]] / 6
30/6 = R
R= 5 ohms

 

[berkeman]

I get 5 Ohms also.

 

[Delta2]

All what you write is mathematically correct but you just playing with algebra and the equation , especially in the last 5 lines of your post.