Least to greatest 66.1%, 0.66, 2/3, 0.666

(method 1) convert them all to fractions of equal denominators
66.1% = 66.1/100 = 1983/3000
0.66 = 66/100 = 1980/3000
0.666 = 666/1000 = 1998/3000
2/3 = 2000/3000

Since 1980 < 1983 < 1998 < 2000, the ascending order should be:
0.66, 66.1, 0.666, 2/3

(method 2) converting them all to decimals
66.1% = 0.661
2/3 = 0.666666666666666

Since 0.66 < 0.661 < 0.666 < 0.666666667, the answer still remains the same:
0.66, 66.1, 0.666, 2/3

25 is obviously the correct answer