It might help to do the translation.
.. % means /100
.. "of" means ×
2. 25% of 12 = 25/100×12 = (25×12)/100 = 300/100 = 3
3. 30% of 20 = 30/100×20 = (30×20)/100 = 6
The rest are worked the same way. Many calculators have a % function that will do this for you.
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Of course, you recognize that
.. 25% = 25/100 = 0.25
.. 30% = 30/100 = 0.30
This conversion of form is often described as "move the decimal point 2 places to the left to convert from a % to a decimal."
