How can a Blackhole have mass? It is said that in Blackhole 100% part of the mass is getting converted into energy. Then how come Blackhole is having mass ?
I believe when most scientists refer to the mass of a blackhole - i.e. a blackhole having the mass of a billion Suns, what they really mean is that the calculated gravitational pull of the blackhole is equivalent to that of such a mass would it exists at the location of the blackhole.

PS: Perhaps you could also bring some reference with respect to where exactly have you heard that 'It is said that in Blackhole 100% part of the mass is getting converted into energy'