UPSC Civil Services 2013 Prelims General Studies Paper II

Let gold coin be represented by ‘G’.
Let non-gold coin be represented by ‘N’.
Initial ratio =

G

N

=

1

3

...(1)
After adding 10 gold coins, the new ratio will be

G+10

N

=

1

2

...(2)
Putting the value of G=

N

3

in equation (2)

N 3 +10

N

=

1

2

On solving, we get N=60
and G=30
Presently, the total number of coins in the collection =10+20+60=90