With input fixed, base resistance changes drive and moves the inverter output.

With input fixed, base resistance changes drive and moves the inverter output. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Sixteen ohms leaves the output near the top

Input stays 5 V while base resistance 16 ohm sets collector current 3/4 A and output 9 V, and checked state MIDDLE.

RB=16 Ω⇒Vout=9 VR_B=16\ \Omega\Rightarrow V_\text{out}=9\ \text{V}
Inverter base-resistance scanThe same input is checked through different base resistors.input 5 Vdrop 1 Vbase 1/4 Adrive 3/4 Aload 3 Acollector 3/4 Aoutput 9 VactiveMIDDLE

Eight ohms pulls the output to the middle

Input stays 5 V while base resistance 8 ohm sets collector current 3/2 A and output 6 V, and checked state MIDDLE.

RB=8 Ω⇒Vout=6 VR_B=8\ \Omega\Rightarrow V_\text{out}=6\ \text{V}
Inverter base-resistance scanThe same input is checked through different base resistors.input 5 Vdrop 1 Vbase 1/2 Adrive 3/2 Aload 3 Acollector 3/2 Aoutput 6 VactiveMIDDLE

Four ohms reaches the low output floor

Input stays 5 V while base resistance 4 ohm sets collector current 3 A and output 0 V, and checked state LOW.

RB=4 Ω⇒Vout=0 VR_B=4\ \Omega\Rightarrow V_\text{out}=0\ \text{V}
Inverter base-resistance scanThe same input is checked through different base resistors.output 0 Vinput 5 Vdrop 1 Vbase 1 Adrive 3 Aload 3 Acollector 3 AsaturationLOW