Question: Which class had a number under 4 and was built in 1988?
SQL: SELECT "Class" FROM "2-1617901-2" WHERE "Number" < 4.0 AND "Built" = '1988';

Question: How many items withdrawn had numbers over 5?
SQL: SELECT COUNT("Withdrawn") FROM "2-1617901-2" WHERE "Number" > 5.0;

Question: What is the sum of numbers that had a type of Driving Van Trailer?
SQL: SELECT SUM("Number") FROM "2-1617901-2" WHERE "Type" = 'Driving Van Trailer';