The first one: the original formula = 3.14× (7.5+2.5) = 3.14×10 = 31.4 (using the inverse operation of multiplication distribution rate).

Second, the original formula = 3.256× (4.298-3.298) = 3.256×1= 3.256 (using the inverse operation of the multiplication distribution rate).

The third one: the original formula = (1000+4) × (1000-4) =1000? -4? =1000000-16 = 999984 (inverse operation using square difference formula)

Fourth: The original formula =(65+35)? = 100? = 10000 (using the complete square formula)