Total Resistance of Parallel Circuit Calculation

[Vaish]

Homework Statement

R1= 9 Ohms R2= 17 Ohms R3= 18 Ohms
what is the total resistance of this arrangement? Express answer in ohms, correct to one decimal place.

Homework Equations

I used the Parallel circuit formula 1/r1 + r2 + r3

The Attempt at a Solution

I got 4.0 Ohms, apparently, it is incorrect. Please help. Thank you!

 

[.Scott]

R1 and R2 are in series, so use the series formula there.
Then the R1R2 resistors are in parallel with R3, so use the parallel formula with the series result and R3.

Also, in the graphic, R3 is 13 ohms, not the 18 you stated.
The "4.05" in the graphic is apparently your answer:
1) Although the problem asks for 1 decimal place, your answer is shown to two places.
2) Your answer is wrong. It is not 4.05 - it is substantially larger than that.

 

[Vaish]

Thank you very much. This definitely helped and I also noted the 1 decimal place.

 

[haruspex]

1/r1 + r2 + r3

No such formula. What did you mean?