Problem: a man swims downstream 28 km and upstream 16 km taking 4 hours each time , what is the speed of the man in still water ?
Rationale: "28 - - - 4 ds = 7 ? - - - - 1 16 - - - - 4 us = 4 ? - - - - 1 m = ? m = ( 7 + 4 ) / 2 = 5.5 answer : e"
annotated_formula: divide(add(divide(16, 4), divide(28, 4)), const_2)