<PRE><B>Question 243093</B>
Let:
r = number of red cards
b = number of blue cards
We are told there are 20 cards, so:
r + b = 20 
which can be rearranged as:
b=20-r
...
Since each r has a value of 3 and each b has a value of 5, we can compute the total.
3r + 5b = 84
...
Substituting,
3(20-b) + 5b = 84
60 -3b +5b = 84
2b=24
b=12
Since the total number of cards is 20, then
r=8
Checking the answer...
3r = 24
5b = 60
24+60=84</PRE>