Explanation:
we need to bring them to the same denominator. in this case : 10
so, 1/10 of everything are red.
1/5 = 2/2 × 1/5 = 2/10 of everything are blue.
so, we now just add these two :
1/10 + 2/10 = 3/10
so, 3/10 are red and blue (rather red or blue, because none are red and blue)..