Explanation:
Let the mass of the compound be 100g.
There are 60.2g of sulfur.
Moles of sulfur
= 60.2g / (32.07g/mol) = 1.877mol
There are 100g - 60.2g
= 39.8g of manganese.
Moles of manganese
= 39.8g / (54.94g/mol) = 0.724mol
Mole ratio of manganese to sulfur
= 0.724mol : 1.877mol = 1 : 2.5.