Question

3. Dunbar bought y bags of Doritos. He bought 5 more bags of pretzels than bags of Doritos. a) How many bags of Doritos and pretzels did he buy? Give your answer in terms of x. b) A bag of Doritos costs 75 cents and a bag of pretzels costs 85 cents. How much money did Dunbar spend? Express your answer in terms of y dollars.

Answer 1

This question gives a system of equations. If we let x = price of a hot dog and y = price of a potato chip, then we can convert the sentences into equations. Think about it, when you buy things, they multiply the price by the number that you buy, then add up all the subtotals. So 4 hotdogs (4 · x) and 5 bags of chips (5 · y) would add together to be to total price $12. Also, 3 hotdogs (3 · x) and 4 bags of chips (4 · y) add together to be the total price of $9.25. Here are the equations:

(1) 4x + 5y = 12

(2) 3x + 4y = 9.25

The best way to solve a system like this is through the elimination method. We want one of the sets of coefficients to line up in such a way that they cancel when we combine the equations. If we multiply equation 1 by 3 and equation 2 by -4, then the coefficients on x with become 12 and -12.

(3) 12x + 15y = 36

(4) -12x - 16y = -37

Adding the equations together reveal a simple equation:

-1y = -1

so y = 1 (A bag of chips cost $1)

Using the fact that we now know the value of y, we can substitute it back into the original equation 1 and them solve for x.

4x + 5(1) = 12

4x + 5 = 12

4x = 7

x = 1.75

so a hot dog cost $1.75.

Answer 2

Solution :

Dunbar bought y bags of Doritos.

He bought 5 more bags of pretzels than bags of Doritos.

This means that he bought y + 5 bags of pretzels .

a) Number of bags of Doritos and pretzels = y + y + 5

⇒ 2 y + 5

We have to represent the above equation in terms of x .

⇒ x = 2 y + 5 .

b) A bag of Doritos costs 75 cents and a bag of pretzels costs 85 cents.

Number of bags of Doritos bought = y .

Cost of doritos = 75 cents × y

1 dollar = 100 cents

⇒ 1 × 75/100 dollar = 75 cents

⇒ 75/100 dollar = 75 cents

⇒ 3/4 dollar = 75 cents .

So equating cost of doritos we get :

⇒ 3/4 × y

⇒ 3 y / 4

⇒ 0.75 y dollars

Bag of Pretzel costs 85 cents

⇒ 85/100 dollars .

There was y + 5 bags .

Cost = 85/100 × ( y+5 )

⇒ 0.85 ( y + 5 )

⇒ 0.85 y + 4.25 dollars .

Total cost in terms of y dollars

⇒ 0.75 y + 0.85 y + 4.25

⇒ 1.6 y dollars + 4.25 dollars .