The same voltage gives less current as checked impedance magnitude grows. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The small triangle gives the largest current
With impedance magnitude 5 ohms, 20 volts gives current 4 amperes.
I=520=4
Doubling the triangle halves the current
The same 20 volts over 10 ohms gives current 2 amperes.
I=1020=2
The largest triangle leaves one ampere
With impedance magnitude 20 ohms, the same voltage gives current 1 ampere.