Choose the cleverest method

There are three methods

to calculate:

 method 1: multiplication first  (2 x 10) : 5 = 20 : 5 = 4
 method 2: fraction first  (2 : 5) x 10 = 0.4 x 10 = 4
 method 3: the other division first  (10 : 5) x 2 = 2 x 2 = 4
Which method is the cleverest to calculate the following expression?

method 1      method 2      method 3




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