So we have two answers to the op's question. Let's vote, toss a coin or derive a new formula to obtain one answer.

Timescope

The RMS is 2.5 Volts.

\(
\mathsf{RMS=V_{pk} \cdot \sqrt{\frac {T_{on}}{T_{on}+T_{off}}}}

\mathsf{RMS=5.0V \cdot \sqrt{\frac{0.25s}{0.25s+0.75s}}}

\mathsf{RMS=5.0V \cdot \sqrt{\frac{0.25s}{1s}}}

\mathsf{RMS=5.0V \cdot 0.500}
\\
\mathsf{RMS=2.5V}

\)

 

Oops. I landed on the wrong side of "Know your sheet or know you're sheet!" that time.

I was thinking of average value.

That's the beauty of forums, and any decent team or community.

Don't worry about making dumb mistakes. Somebody will probably notice it fairly quickly.

 

So we have two answers to the op's question. Let's vote, toss a coin or derive a new formula to obtain one answer.

Timescope

There is no vote required. I already showed how to calculate RMS in post #8.

 

There is no vote required. I already showed how to calculate RMS in post #8.

So let's take 16 samples of the waveform during 1 period. The first 4 samples are 5v and the remaining 12 are zero. Squaring each sample and adding them together we get

25 +25 +25 +25 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 +0 = 100

The average is 100/16 =6.25 and the rms value is √6.25 = 2.5v

Timescope

 

Bingo!!!!!