Answer :
Sand is 1/6 of the mixture. 1/6 x 1800 = 300 kg
Gravel is 2/6 of mixture. 2/6 x 1800 = 600 kg
Cement is 3/6 of mixture. 3/6 x 1800 = 900 kg
Gravel is 2/6 of mixture. 2/6 x 1800 = 600 kg
Cement is 3/6 of mixture. 3/6 x 1800 = 900 kg