This is something you should memorize. Specifically it is from the Empirical Rule (or 68-95-99.7 rule) which gives rough approximations of areas under the curve.
You save ⅓ of entry fee, so you save 1.20 and you pay 2.40. We only really care about the 1.20 reduction. 5 / 1.2 = 4.16 so he must go 5 times to get the 5 back