< means 'less than' and > means 'more than'
SO
Ten is less than fifteen would be written … 10 < 15
Yes.
15/10000 or 0.0015
10-15
0.00001
15.9994
15.9994 amu
0.0004
0.0004
0.0004
0.0004
0.00045 ten-thousandths is 0.0005. You can write any number which has 4 or less in place of the 5, and any numbers you want after that. Another example would be 0.000357915.
15 less than y the difference of 15 and y