100 kg hard water contains 5 g mgso4.the hardness of sample water in ppm of caco3 is

Dear student 
we need to calculate the hardness of 5mg of Mgso4 present in 1 kg of water , 
so, here 
given , 1000g of water contains Mgso4 = 5 mg 
1000000g of water contain mgso4 = 5 * 1000 = 5000 mg = 5g 
u need to remember – 100000g = one million parts of water 
1 mole of mgso4 = 1 mole of caco3 
120 g of mgso4 = 100g of caco3 
5 g of mgso4 = (100g * 5 g ) / 120 g of caco3 = 4.16g of caco3 
so, here degree of hardness =  4.16ppm

Regards