Question

a jar contains 10 red and 30 green.how many marbles shud b added to it so dat 60%
marbles r red?

Answer 1

I will assume you meant, "How many red marbles should be added"

let the reds to be added be x
so we have 10+x reds
total = 40+x

(10+x)/(40+x) = (3/5)
50 + 5x = 120 +3x
2x = 70
x = 35

#5 reds should be added

check:
reds = 45
total = 75

percentage of reds = 45/75 = .6 or 60%