If the entire race is 40 miles, then the second checkpoint is 3/4 of the whole way, which is 30 miles because 40 ÷ 4 = 10 and 10 x 3 = 30. This means that there are 30 miles between the start and the second checkpoint. 2/5 of 30 is 12 because 30 ÷ 5 = 6 and 6 x 2 = 12. Therefore, the answer is 12 miles