[1.8] vainilla zombie default spawn rate ??

good nigths i been working in some zombies and i want this two zombies to spawn in same amount and same places than vainilla zombies

but du not know the rigth values  , i now its some where in references library but dont find it

can someone tell what the values for the vainilla zombie are 

values im currently using but the spawn is less than espected

if (this.zombie){

EntityRegistry.addSpawn(mercenarymod.entidades.hostiles.zombieMercenario.class, 60, 1, 10, EnumCreatureType.MONSTER, allBiomes);

}

if (this.zombieR){

EntityRegistry.addSpawn(mercenarymod.entidades.hostiles.zombieMercenarioE.class, 80, 1, 10, EnumCreatureType.MONSTER, allBiomes);

}