Problem: the average age of a family of 6 members is 26 years . if the age of the youngest member is 10 years , what was the average age of the family at the birth of the youngest member ?
Rationale: "present age of total members = 6 x 26 = 156 10 yrs back their ages were = 6 x 10 = 60 ages at the birth of youngest member = 156 - 60 = 96 therefore , avg age at the birth of youngest member = 96 / 6 = 16 . answer : c"
annotated_formula: subtract(divide(subtract(multiply(6, 26), 10), const_4), 10)