stock Interest(Float:q,Float:s) return floatround(s*100.0/q);

public OnPlayerGiveDamage(playerid, damagedid, Float: amount, weaponid, bodypart)
{
    new Float:Health,string[55];
    GetPlayerHealth(damagedid, Health);
    format(string,sizeof(string), "Ты получил %i/% урона", Interest(Health, amount);
    SendClientMessage(damagedid, -1, string);
    return 1;
}