Two sisters want to buy a pack of buttons for different craft projects. Alice wants a design which requires 18 buttons, while Mary wants a design which requires 20 buttons. By applying your knowledge of the Highest Common Factor or Lowest Common Multiple, choose the most suitable HCF or LCM and justify your choice with a brief explanation. Hence or otherwise, determine the number of buttons in the smallest packet possible, enabling both designs to use all buttons without leaving
leftovers. (7)