Finding some percentages is fairly easy.
Both double digits and end with "0".
20% of 50=?
Simply multiply 2x5, answer is 10.
70% of 90=63
80% of 50=40
Single digit percentages and number ends with "0" you only need to multiply and stick a decimal between your answer.
9% of 50. 9x5 (45) 4.5
7% of 90= 7x9 (63) 6.3
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A little more complicated.
Only one of the numbers ends with zero (0).
71% of 50? Multiply 7x5 (35) put a decimal, then multiply 1x5 (5). Answer: 35.5
20% of 14? 2x1 (2), 2x4 (8) = 2.8
30% of 11=3.3