He was told 10 cookies and 18 scones will cost $36, but 15 cookies and 13 scones will cost $40. How much is one cookie

Question

10 cookies and 18 scones will cost $36 and 15 and 13 scones will cost $40.

Answer 1

c = cost of a cookie

s = cost of a scone

 

10c + 18s = 36   {equation 1}

15c + 13s = 40   {equation 2}

 

Let's eliminate s to solve fo c.

Multiply equation 1 by 13

Multiply equation 2 by -18

Add equations to eliminate s

 

  130c + 234s = 468

-270c - 234s = -720

----------------------------

-140c = -252

c = (-252)/(-140)

c = $1.80 per cookie