A sum doubles itself in 6 years at simple interest. in how many years will the sum become 8 times of itself at the same rete of interest.

• 42 yrs
  
  In 6 years , interest will be 1 times the principal
  For interest to be 7 times principal at same rate of interest, time will be 7 times i.e. 7*6=42 years
  
  rate of interest = x*100/6x= 50/3%
  then
  7x= x*(50/3)*t/100
  t= 7*3*100/50= 42 yrs
• 11 years agoHelpfull: Yes(0) No(0)
• 42 yrs,
  let the Principal = Rs. 100.
  SI after 6 yrs = Rs. 100
  Since R= SI X 100 / P X T i.e R = 100 X 100 / 100 X 6 = 50/3 %
  Now when the sum becomes 8 times , SI = 700, P=100, R= 50/3, T= ?
  T=SI X 100 / P X R = 700 X 100 / 100 X 50 / 3 = 42 Yrs Ans.
• 11 years agoHelpfull: Yes(0) No(0)
• 24 years..,
  let x be the sum..
  after 6 years it becomes 2 times x...so,2x..
  after another 6 years it becomes 2x...
  after another 6years it becomes 2x...
  after another 6 six years it becomes 2x...
  now x becomes 8x...number of years...6+6+6+6=24 years..
• 11 years agoHelpfull: Yes(0) No(0)
• note: (n1-1)/t1=(n2-1)/t2
  
  n1=2;t1=6;n2=8;t2=......
  (2-1)/6=(8-1)/t2
  1/6=7/t2
  t2=42.
• 8 years agoHelpfull: Yes(0) No(0)