3 * * * has 33 multiples and 5 has 20 multiples. Note the six common multiples of 3 and 5 * * *. That is, in the number of 100, 27 is a multiple of 3 and 14 is a multiple of 5. Considering that if a number is randomly added from a multiple of 3 and a multiple of 5, it is possible to get a common multiple of both, so that the sum is the same, but adding a multiple of 3 and a multiple of 5 will not get the same answer, so the correct answer should be 27* 14+6*5/2=393. The latter term is the possibility of choosing two common multiples of 3 and 5.