there are some red counters and some yellow counters in the ratio 1:5. There are 20 yellow counters

There are some red counters and some yellow counters in the ratio 1:5. There are 20 yellow counters in the bag.

Set up a proportion where x is the amount of red counters to 20 yellow counters
1/5 = x/20

Enter that in the search engine and our proportion calculator gives us:
x = 4