
Sam K. answered 02/24/23
Harvard MBA - Algebra I/II, Precalc, ACT/SAT Math, Geometry, TOEFL
So let X = the number of adult tickets and Y = the number of kids' tickets
The total number of tickets is 12
Thus X + Y = 12 .......................Equation 1
The total cost for adult tickets is $9.5 times X or 9.5X dollars
The total cost for kids' tickets is $6.5 times Y or 6.5Y dollars
Since $87 was the total cost then
9.5X + 6.5Y = 87 .........................Equation 2
So now we have two equations in two unknowns (X and Y). We can solve for the X and Y in different ways. We will use the method of substitution in this case.
Since the question asks for the number of kids' tickets we will solve for Y. From Equation 1, let's find X
X + Y = 12
Subtract Y from both sides to get X + Y - Y = 12 - Y
Thus X = 12 - Y .............Equation 3
Substituting Equation 3 in Equation 2 we get
9.5(12-Y) + 6.5Y = 87
9.5*12 - 9.5*Y + 6.5Y = 87 (We are using the * symbol to denote multiplication)
114 - 3Y = 87
subtract 114 from both sides to get
114-3Y - 114 = 87 - 114
-3Y = -27 and dividing both sides by -3 we get
-3Y/-3 = = -27/-3
Y = 9 or the total number kids' tickets is 9 is your answer.
You can quickly check your answer to see. Total tickets were 12 so the adults tickets were then 3 from
(12 -9)
And for the cost you have 9.5*3 + 6.5*9 = 28.5 + 58.5 = $87