Are you people getting it!!? - Marisa

We're just an ordinary magician and an ordinary kappa! - Marisa

And our opponents are a Hakurei shrine maiden and a vampire!! - Marisa

And our opponents are a Hakurei shrine maiden and a vampire!! - Marisa

Won't we be decimated at once by default!? - Marisa

But we're still fighting here!! - Marisa

We're struggling and fighting!! - Marisa

We're struggling and fighting!! - Marisa

Say something, all of ya!! - Marisa

Haven't you ever had any painful memories of being powerless at all!? - Marisa

Fight fair and square, and then lose? - Marisa

Fight fair and square, and then lose? - Marisa

To hell with that!! - Marisa

So that's what she's going to do...

... what do you think are the odds that she'll fail? Nanwari, in this case, means ratio out of ten. Thus, Yukari is saying 30% chance of failing here.

Episode 742: The Value of a Virtue From the Artist's Pixiv page.