5g of crystalline salt rendered anhydrous lost 1.89g of water . the formula weight of the anhydrous salt is 160 . the number of water molecule on crystallization are

Given,
5g of a crystalline salt when rendered anhydrous lost 1.8g of water
Therefore,
Amount of anhydrous salt left = 5 -1.8 = 3.2 g
Molecular weight = 160 g/mol
Thus,
Number of moles of anhydrous salt = (3.2g) / (160 g/mol)
=  0.02 moles
Mass of water lost = 1.8 g
Molar mass of water  = 18 g/mol
Thus,
Number of moles of water = (1.8g) / (18 g/mol)
=  0.1 moles
Ratio of the anhydrous salt to water is ,
Salt : Water
= 0.02 moles : 0.1 moles
Divide by the smallest number,
(0.02 moles / 0.02)  :  (0.1 moles / 0.1)
1  :  5
Hence,
The number of molecules of water of crystallisation in the salt = 5 H2O