Question

Chalk contains calcium,carbon and oxygen in the ratio 10:3:12.Find the percentage of carbon in a chalk and in a stick of chalk, carbon in 3g what is the length of chalk stick?

Answer 1

no idea what the length of the chalk stick is, since you have given neither density nor size.

All we know is that the carbon is 3/25 = 12% of the total mass.

Answer 2

carbon is 3/25 = 12/100 = 12%

No idea. You did not tell me the diameter of the stick.