Question Number 104876 by mathocean1 last updated on 24/Jul/20
$${A}\:{ballot}\:{box}\:{contains}\:\mathrm{7}\:{balls}\left(\mathrm{3}\:{are}\:\right. \\ $$$$\left.{black}\right).\:{we}\:{draw}\:{successively}\:{and} \\ $$$${reputing}\left({inside}\right)\:\mathrm{5}\:{balls}. \\ $$$${What}\:{is}\:{the}\:{number}\:{of}\:{possibilities}\: \\ $$$${to}\:{have}\:{one}\:{black}\:{ball}? \\ $$