I can't help you with the missing length, since you haven't told me anything about the shape of whatever has the missing length. As for the rounding...
Sometimes it is advantageous to express a value in round numbers. To round to a particular place, look at the digit immediately to the right of the one you want to round to, in this case, the ones place. If that digit is 4, 3, 2, 1 or 0, zero it and everything to the right of it out. If that digit is 5, 6, 7, 8 or 9, increase your target digit by one and zero everything to the right of it out. If your target digit is 9, it will become a zero and increase the digit to the left of it by one.
11.70
LM = 4 in LN = ? Find LN. Round the answer to the nearest tenth.
Only if you were asked to find the mean to the nearest tenth. If so, don't round each number; calculate the mean first and then round it to the nearest tenth.
Round to the nearest cent.
Say you approximate a length of a line.approximation to the nearest ten means you find the tens column. e.g.25632 - in this case the '32'then you round it. to 25630from 0 - 4 you round downwards, from 5 - 9 you round upwards so...248 goes to 250 for example.
To find the missing length of a triangle
Of what?
Round to the nearest dollar.
2.3
Round the number to the nearest tenth.
5.1 cm
The word round in maths means to find the nearest value of a number.