The picture on the left shows a DC voltage source connected with 3 parallel-connected resistors. The question is again: what is the total resistance?

The current in R1 (I1) equals to: I1 =
V_{bat}/R1. And I2 = V_{bat}/R2,
and V3 = V_{bat}/R3. The total current
I_{tot} equals I1 + I2 + I3, so:

I_{tot} = V_{bat}/R1 +
V_{bat}/R2 + V_{bat}/R3.

This proves that the total resistance of parallel connected resistors equals to:

1/R_{tot} = 1/R1 + 1/R2 + 1/R3 + ... or:

In this case, the total resistance is 333Ω. The total current will be 3 ∙ 9mA = 27mA.