A bag contain marbles of three different colours red blue and yellow 2/5of the marbles are red the ratio of three number of blue marbles to the number of yellow marbles is5:7 what fraction of the marbles in the bag is blue

Answer 1

Let's say there are m marbles.
The clues given are:
b+r+y = m
r/m = 2/5
b/y = 5/7

r = 2m/5
y = 7b/5

so

b+r+y = m
b+(2m/5)+(7b/5) = m
12b/5 = 3m/5
b/m = (3/5)(5/12) = 1/4

Answer 2

m marbles in bag
2m/5 are red
so
3 m/5 = b+y
m = r + b + y

b/y = 5/7
or y = 7b/5

3 m/5 = b + 7b/5
3 m/5 = 12 b/5
4 b = m
b = (1/4) m