A customer at a bakery paid $78.30 for donuts and cupcakes. Each donut cost $1.95 and each cupcake cost $2.85. If they bought a total of 30 donuts and cupcakes, how many donuts did they buy?

  (1)

  (2)

From equation (1) we can solve for x and we got:

(3)

Replacing (3) into (2) we got:

And solving for y we got:

And then solving for x we got:

So then we have 8 donuts and 22 cupcakes

Step-by-step explanation:

Let x the number of donuts and y the number of cupcakes, from the info given we can set up the following equations:

  (1)

  (2)

From equation (1) we can solve for x and we got:

(3)

Replacing (3) into (2) we got:

And solving for y we got:

And then solving for x we got:

So then we have 8 donuts and 22 cupcakes

17

step-by-step explanation:

{x = -1/2 ,   y = -1

step-by-step explanation:

solve the following system:

{2 x + y = -2

{10 x - 3 y = -2

in the first equation, look to solve for y:

{2 x + y = -2

{10 x - 3 y = -2

subtract 2 x from both sides:

{y = -2 x - 2

{10 x - 3 y = -2

substitute y = -2 x - 2 into the second equation:

{y = -2 x - 2

{10 x - 3 (-2 x - 2) = -2

10 x - 3 (-2 x - 2) = (6 x + 6) + 10 x = 16 x + 6:

{y = -2 x - 2

{16 x + 6 = -2

in the second equation, look to solve for x:

{y = -2 x - 2

{16 x + 6 = -2

subtract 6 from both sides:

{y = -2 x - 2

{16 x = -8

divide both sides by 16:

{y = -2 x - 2

{x = -1/2

substitute x = -1/2 into the first equation:

{y = -1

{x = -1/2

collect results in alphabetical order:

answer:   {x = -1/2 ,   y = -1