“The answer is 0.30000000000000004 (the second one) because its significand is even.”
The exact sum of the 64-bit values for 0.1 and 0.2 lands precisely halfway between two floats. IEEE 754 breaks the tie toward the even significand, and that one prints as 0.30000000000000004. Every programmer has seen this. Almost nobody can explain it, and it all comes down to a tiebreak rule.