Question

A bag holds 1 blue block and 3 yellow blocks. How
many green blocks should be added to the bag to make
the probability of randomly selecting a green block
from the bag equal to 1/2?

Answer 1

1 block + 3 blocks = 4 blocks total
you need to add 4 green blocks so the total is now 8 blocks and 4 is half of 8
hope you understand this :)