51.a guy has three type transactions on his checking account, type A, each time deposit $500 ;type B, each time deduct 400 dollars, type C each time deduct 300 dollars. Ask if this guy made at least 10 times of transactions total in a month. A) this guy at least made 1 time type A, 1 time type B and 1 times of Type C transaction in a month B) this guy has $1600 more on his checking account than last month. C:综合(A)(B)可知最小的次数是500 6次,400 2次,300 2次。