harish had 30 pieces of sweets. if he ate 7/10 of them each day, how many sweets will be left after a month?

he  had pieces of sweets = 30
he ate each day = 7/10 
so,
      10*3=30
      7*3=21
so,
   he ate 21/30 pieces of sweets each day..
sweets left after a month = 30-21*no.of days in months
therefore,30-21*30
              =9*30
             =270sweets..... 
i hope this will make you understand this question..