My mental process: Well it's less than 100 since 100^2 = 10,000 so that goes over. It's over 10 since 10^3=1000. So this narrows it to more than 10 and less t

My mental process: Well it's less than 100 since 100^2 = 10,000 so that goes over. It's over 10 since 10^3=1000. So this narrows it to more than 10 and less than 100. log-wise 30 is about midway between 10 and 100. 900 x 30 is is 27000 so it's less than 30. 20? 400 x 20 = 8000 so bigger than that. Then it gets annoying to compute the cubes so close enough to say more than 20 and less than 30.