Technically, its not correct as stated. It is better stated as
100+100+100+100=5.
When you use (5^1/2)/2 as a base, its about 1.1 so its similar to binary in that technically only 1's and 0's are allowed. If you use 5^1/2 as a base, that is 2.2 and change so you would be ok using 0,1,and 2. In that base it would be correct to say 100(B Sqrt5)=5(B10)