4+4 = 8
It can be but normally IV = 5-1 = 4
You can for the numeral IIII representing 4 but even that is normally written as IV, other than that generally no. 40 = XL, 400 = CD and 4000 = (IV)
7 is 3 larger than 4.
Some Roman numeral clocks use IIII to represent 4, which is how most Romans would have written it. However, in order to comply with the rule that no numeral should be writen more than three times in succession the number 4 is now more correctly written as IV.
8010
Generally the Roman numeral IV represents the number 4 but on some old watches and sun dials 4 is represented by the numeral IIII. The numeral IIII was correct when it was written but convention now decrees that a numeral should not be repeated more than three times. According to this rule IIII should no longer be used.
If you're meaning 9.21 x 10-4 than the standard numeral would be 0.000921.
4. The roman numeral for 4 is IV.
500
9100
It is: 1900+1000 = 2900
2100 + 10 = 2110