Question 889905
Present age of Joana=11
Present age of mother=31
After some years mother's age is twice as that of joana's.Let the number of years be n
         Thus, 31+n=2(11+n)
               31+n=22+2n
                 31-22=2n-n
                Therefore,n=9
Check:mother's age after 9 years           
          =31+9=40
   Joana's age after 9 years=11+9=20
Joana's mother is twice as old as her after 9 years