Problem: a man whose speed is 6.5 kmph in still water rows to a certain upstream point and back to the starting point in a river which flows at 1.5 kmph , find his average speed for the total journey ?
Rationale: "m = 6.5 s = 1.5 ds = 8 us = 4 as = ( 2 * 8 * 4 ) / 12 = 5.33 answer : a"
annotated_formula: divide(add(6.5, subtract(6.5, 1.5)), const_2)