Final answer:
To mentally calculate what percentage one number is of another, divide the first number by the second number and multiply by 100.
Step-by-step explanation:
To calculate what percentage one number is of another, you need to divide the first number by the second number and then multiply by 100. In this case, to find out what percentage 15 is of 30, divide 15 by 30 and then multiply by 100.
15 ÷ 30 = 0.5
0.5 × 100 = 50%
Therefore, 15 is 50% of 30.
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