How many coins does she have of each kind?

Question

Ana has 49 copper and silver coins in her collection. She got quite a few of them on her birthdays. She has 13 fewer copper coins than silver coins in her collection. How many coins does she have of each kind?

Answer 1

c = s - 13

s + c = 49

 

Two different methods jump out at me. First, since c = s - 13, we can substitute s - 13 for c in the 2nd equation.

 

s + (s - 13) = 49

2s = 62

s = 31

 

c = 31 - 13

c = 18

 

Second, solve the 2nd equation for c.

 

c = 49 - s

 

Now, since c = 49 - s and c = s - 13, they equal each other.

 

49 - s = s - 13

2s = 62

s = 31

 

c = 31 - 13 

c = 18

 

Pick which is better for you!