Question

(HELP ASAP PLEASE)

Solve using any method and fill in the blanks.

Lloyd's Bakery sold one customer 9 dozen chocolate cookies and 8 dozen oatmeal cookies for $110. The bakery also sold another customer 9 dozen chocolate cookies and 5 dozen oatmeal cookies for $89. How much do the cookies cost?

A dozen chocolate cookies cost $___ and a dozen oatmeal cookies cost $___

Answer 1

A dozen chocolate cookies cost $6

and a dozen oatmeal cookies cost $7

Explanation:

Let's assume that cost of 1 dozen chocolate cookies = x

Let's assume that cost of 1 dozen oatmeal cookies = y

then we get equations:

9x+8y=110...(i),

and 9x+5y=89...(ii)

Solve equation (i) for x

9x+8y=110

9x=110-8y

`x=(110-8y)/(9)`...(iii)

plug (iii) into (ii)

9x+5y=89

`9\left((110-8y)/(9)\right)+5y=89`

`110-8y+5y=89`

`9\left((110-8y)/(9)\right)+5y=89`

`110-3y=89`

`-3y=89-110`

`-3y=-21`

`y=7`

plug y=7 into (iii)

`x=(110-8y)/(9)=(110-8(7))/(9)=6`

So the final answer is given by:

A dozen chocolate cookies cost $6

and a dozen oatmeal cookies cost $7