No, a half-marathon is NOT “more than four times longer than” a 5K. It is more than four times AS LONG AS a 5K. In order for it to be four times longer than a 5K, it would need to be the length of one 5K plus an additional four times the length of one 5K, in other words 1x5K+4x5K, or 25K total, which it isn’t.