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
420.0
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
Rounded down to the nearest tenth, 43.7002 is equal to 43.7.
5.1
0.4
0.3
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.
The tenth place is the first number after the decimal. To round, 5 and up will be rounded up and 4 and lower will be rounded down. The tenth decimal place of 0.621 is 6. The two is 4 or lower so it will be rounded down to 0. Therefore, 0.621 to the nearest tenth is: 0.6