SOLUTION: Galina spent $3.60 for stamps to mail packages. Some were 30 cents and the rest were 20 cents. The number of 20 cent stamps is two less than the 30 cent stamps. How many stamps of

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Galina spent $3.60 for stamps to mail packages. Some were 30 cents and the rest were 20 cents. The number of 20 cent stamps is two less than the 30 cent stamps. How many stamps of       Log On


   

Question 699611: Galina spent $3.60 for stamps to mail packages. Some were 30 cents and the rest were 20 cents. The number of 20 cent stamps is two less than the 30 cent stamps. How many stamps of each kind did Galina buy?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +a+ = number of 30 cent stamps she bought
Let +b+ = number of 20 cent stamps she bought
given:
(1) +30a+%2B+20b+=+360+ ( in cents )
(2) +b+=+a+-+2+
---------------
Substitute (2) into (1)
(1) +30a+%2B+20%2A%28+a+-+2+%29+=+360+
(1) +30a+%2B+20a+-+40+=+360+
(1) +50a+=+400+
(1) +a+=+8+
and, since
(2) +b+=+a+-+2+
(2) +b+=+8+-+2+
(2) +b+=+6+
She bought 8 30 cent stamps and 6 20 cent stamps
check:
(1) +30%2A8+%2B+20%2A6+=+360+
(1) +240+%2B+120+=+360+
(1) +360+=+360+
OK