a is three times as fast as b . if b alone can do a piece of work in 12 days , in what time can a and b together complete the work ?
"a can do the work in 12 / 3 i . e . , 4 days . a and b ' s one day ' s work = 1 / 4 + 1 / 12 = ( 3 + 1 ) / 12 = 1 / 3 so a and b together can do the work in 3 days . answer : c"
inverse(add(inverse(divide(12, const_4)), inverse(12)))