In 1 Kg mixture of sand and iron, 20% is iron. How much sand should be added so that proportion of iron become 10%.

1 Kg=1000 g
Amount of Iron in mixture=20% of Sand
20/100*1000=200 g
Amount of Sand=1000-200=800g
Let the sand added “x”
Iron=10/100(1000+x)
200=1/10(1000+x)
2000=1000+x
2000-1000=x
1000=x