Technically no, because pi equals pi not 5. But you can approximate its value as 3 or 5 or whatever you want, knowing it’s not exact and that your result will only be an approximation. I mean you could also ask how long light takes to reach us from Alpha Centauri if the speed of light is 1000 mph. It’s not, but if you make that a condition of the problem you can do the calculation just fine.