Rounded down, 66.38 is approximately equal to 66.3 - though ordinarily you would not round the number down, as the final digit is greater than 5.
10.9
You would round it down to the nearest tenth, 4.5.
2.4 is rounded down to 2.3 * * * * * 2.4, to the nearest tenth, is 2.4!
3.5
0.1
Rounded down to the nearest tenth, 43.7002 is equal to 43.7.
5.1
0.3
0.4
0.4 is equal to 4/10, or four tenths. No further rounding is required - it is already rounded down to the nearest tenth.
Rounded down to the nearest tenth, 13.4256 is approximately equal to 13.4, or 13 and four tenths.
40.3