ANSWERS: 3

let the cost of the meal is = x now x*112/100*115/100=128.80 now solve the above equation

You can use cross multiplication to enter the known information: tax / meal = (12/100) ;;; tip(meal) / meal = (15/100) ;;; tip(tax) / tax = (15/100) ;;; Use substitution to get the total sum to pay as a function of the meal price: Total = meal + tax + tip(meal) + tip(tax) ;;; Total = meal + (12/100) X meal + (15/100) X meal + (15/100) X tax ;;; Total = meal + (12/100) X meal + (15/100) X meal + (15/100) X (12/100) X meal ;;; Total = meal X [1 +(12/100) +(15/100) +(15/100)X(12/100)] ;;; Total = meal X [1 + 0.12 + 0.15 + 0.018] ;;; Total = meal X [1.288] ;;; On the other hand, Total = $128.80 ;;; $128.80 = meal X [1.288] ;;; meal = $128.80 / 1.288 = $100

5182017 If the teacher wants that method, it is the teacher's job to teach it. Math always has been and always will be a matter of pattern recognition, which means a duffer might recognize a method that nobody noticed before. That happens all the time.
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