Problem: the average earning of a person for the first 4 days of a week is rs 18 and for the last 4 days is rs 22 . if he earns rs 20 on the fourth day , his average earning for the whole week is ?
Rationale: total earning for the week = rs ( 4 × 18 + 4 × 22 - 20 ) = rs 140 average earning = rs 140 / 7 = rs 20 . answer : c
annotated_formula: divide(subtract(add(multiply(4, 18), multiply(4, 22)), 20), add(const_4, const_3))