Answer:
# of 20cent stamps = 8
Step-by-step explanation:
Let the number 20cent stamps be = x
Let the number 60 cents stamps be = y
Total number of stamps => 20 = x + y ----------- ( 1 )
Total cost of the stamps = 8.80
That is, 0.20x + 0.60y = 8.80 ------------- ( 2 )
( 2 ) => 20x + 60y = 880
=> x + 3y = 44
=> x = 44 - 3y
Substitute x in ( 1 ) => x + y = 20
44 - 3y + y = 20
- 2y = 20 - 44
- 2y = - 24
2y = 24
y = 12
Substitute y = 12 in ( 1 ) => x + y = 20
x + 12 = 20
x = 8
