There is only black pens and green pens in a box the ratio of the number of the black pens in the box of the number of green pens in the box

Question

1:4 is the ratio but I need to see what fraction of the pens are black 

Answer 1

Suppose there are 100 pens in the box in the ratio 1 black for every 4 green.

This would mean 20 black and 80 red.

20/100=1/5