Answer:
There are 12 purple marbles and 8 yellow marbles.
Step-by-step explanation:
Let there are x purple and y yellow marbled in a bag.
x+y = 20 ...(1)
The number of purple marbles is 4 less than 2 times the number of yellow marbles.
x = 2y -4
x-2y = -4 ...(2)
Subtract equation (1) from (2).
x-2y-(x+y) = -4-20
-2y-y = -24
-3y = -24
y = 8
Put the value of y in equation (1).
x+8 = 20
x = 12
Hence, there are 12 purple marbles and 8 yellow marbles.