3/8 of a pie means that there are 8 pieces originally, and 3 of them are taken.
DECIMAL;
To find the decimal, divide 3 and 8.
3/8 = 0.375 (if you need to round it....0.4)
PERCENT;
To find the percent multiply the decimal by 100%.
3/8 = 0.375 (rounded 0.4)
0.375 * 100% = 37.5% (0.4 * 100% = 40%)