Still wrong. Let me show you how it's done.
1 (b10) = 1
1 (banything) = 1
10 (b10) = 10
10 (b8) = 8
10 (b5) = 5
20 (b10) = 20
20 (b8) = 16
20 (b5) = 10
100 (b10) = 100
100 (b8) = 64
100 (b5) = 25
10 (b54) = 54
EDIT: Also,
anything (banything) generally cannot exist
eg. 6 (b6) cannot exist, 9 (b9) cannot exist
1 (b1) technically cannot exist either.
12 (b12) and 99 (b99) and similar cases can exist however because they're not represented as single digits. However, they do represent completely different numbers to 12 (b10) and 99 (b10)