You can solve it, however, by knowing that 5√2 < 5 * 1.45 = 7.2 (either because √2 = 1.414... is well known, or 1.45^2 = 2.125 is easy because 1.45^2 = 1.

You can solve it, however, by knowing that 5√2 < 5 * 1.45 = 7.2 (either because √2 = 1.414... is well known, or 1.45^2 = 2.125 is easy because 1.45^2 = 1.41.5 + .0025) 2√13 > 2√12.96 = 2 * 3.6 = 7.2 (36^2 = 6^4 = 1296 is a common fact from dice probability.) P.S: 0.45^2 = .2025 and 1.45 = 2.125 is an amusing coincidence.