Question

Anne, Barry, and Cathy enter a coffee shop. Anne orders two coffees, one juice, and two doughnuts and pays $7.50. Barry orders one coffee and three doughnuts and pays $5.00. Cathy orders three coffees, one juice, and four doughnuts and pays $11.50. Find the price of coffee, juice, and doughnuts at this coffee shop.

Answer 1

Answer:

Coffee = $2.00

Juice = $1.50

Doughnut = $1.00

Step-by-step explanation:

Given

Let:

$c = coffee\\ j= juice\\ d = doughnut$

So, we have:

Anna

$2c + j + 2d = 7.50$

Barry

$c + 3d = 5.00$

Cathy

$3c + j + 4d = 11.50$

Required

The price of each

We have:

$2c + j + 2d = 7.50$

$c + 3d = 5.00$

$3c + j + 4d = 11.50$

Make c the subject in: $c + 3d = 5.00$

$c = 5.00 - 3d$

Substitute $c = 5.00 - 3d$ in $2c + j + 2d = 7.50$ and $3c + j + 4d = 11.50$

$2c + j + 2d = 7.50$

$2[5.00 - 3d] + j + 2d = 7.50$

$10.00 - 6d+ j + 2d = 7.50$

Make j the subject

$j = 7.50 - 10.0 +6d - 2d$

$j = -2.50 +4d$

$3c + j + 4d = 11.50$

$3[5.00 - 3d] + j + 4d = 11.50$

$15.00 - 9d + j + 4d = 11.50$

Make j the subject

$j = 11.50 - 15.00 + 9d -4d$

$j = -3.50 + 5d$

So, we have:

$j = -3.50 + 5d$ and $j = -2.50 +4d$

Equate both values of  j

$-3.50 + 5d = -2.50 + 4d$

Collect like terms

$5d - 4d = 3.50 -2.50$

$d = 1.00$

Substitute $d = 1.00$ in $j = -3.50 + 5d$

$j = -3.50 + 5d$

$j = -3.50 + 5 * 1.00$

$j = -3.50 + 5.00$

$j = 1.50$

To solve for c, we substitute $d = 1.00$ in $c + 3d = 5.00$

$c + 3 * 1.00 =5.00$

$c + 3.00 =5.00$

Solve for c

$c =- 3.00 +5.00$

$c =2.00$