a sum of money doubles itself in 4 years at c.i .it will amount to 8 times itself at the same rate of interest in how many years

• 2^1/4= 2^3/x
  1/4=3/x
  x=12 years
• 7 years agoHelpfull: Yes(5) No(0)
• 28. i dont want to write. i can use that time to solve another question
• 7 years agoHelpfull: Yes(1) No(7)
• Let,
  Principal = Rs. 100.
  Amount = Rs. 200.
  Rate = r%
  Time = 4 years.
  Now,
  A = P*[1+ (r/100)]n;
  200 = 100*[1+(r/100)]4;
  2 = [1+(r/100)]4; ........... (i)
  If sum become 8 times in the time n years,
  then,
  8 = (1+(r/100))n;
  23 = (1+(r/100))n; ........ (ii)
  Using eqn (i) in (ii), we get;
  ([1+(r/100)]4)3 = (1+(r/100))n;
  [1+(r/100)]12 = (1+(r/100))n;
  Thus, n = 12 years.
• 7 years agoHelpfull: Yes(0) No(0)