At what rate of annual simple interest,a certain sum will amount to four times in 15 year?

(a)15%
(b)17.5%
(c)20%
(d)25%

• r=?
  t=15 yrs
  
  SI=p*r*t/100
  Amount = SI+p = 4p
  (p*r*15/100)+p = 4p
  p(15r/100 + 1) = 4p
  15r + 100 = 400
  15r = 300
  r = 20%
  
  Ans : (c) 20%
  
  
• 10 years agoHelpfull: Yes(11) No(0)
• Rule of 72 say if you take any interest rate and divide it into 72 it tells you how long before you money doubles. so 72/15%= 4.8 years so in 9.6 years your money is over 4 times its value. verify by using following equation:
  Principle( 1+ rate/annualcompunding)^years:
  10000(1+.15/1)^15= $81370 this is more than 4 times $10,000
• 10 years agoHelpfull: Yes(0) No(2)
• Ans-c 20%
  (P*r*15)/100+p=4p
  P(3r+20)=80p
  R=20%
• 7 years agoHelpfull: Yes(0) No(0)