Chalk contains 10% calcium, 3% carbon and 12% oxygen. Find the amount of carbon, calcium and oxygen in 1 kg of chalk.

Given, Percentage of calcium = 10%

Percentage of carbon = 3%

Percentage of oxygen = 12%

Total percentage of calcium, carbon and oxygen in chalk = 10% + 3% + 12% = 25%

$\therefore$Total amount of calcium, carbon and oxygen = 25% of 1000g (1kg = 1000g)

$=$ $\frac{25}{100} \times 1000g$

$=$250g.