If f(x+y)=f(x)*f(y) and f(1)=1.6 and f(1)+f(2)+.....+f(n) is between 24 to 27. Then find the value of n.

• N= 5
  It forms a G.P like ........1.6 + (1.6)^2+(1.6)^3.....(1.6)^n whose sum is
  1.6*((1.6)^n-1)/(1.6-1) which should be between 24 and 27 solving it we get n= 5
• 11 years agoHelpfull: Yes(20) No(2)
• f(1)=1.6
  f(1+1)=1.6*1.6,f(2)=1.6*1.6
  similarly,f(3)=1.6*1.6*1.6
  f(4)=1.6*1.6*1.6*1.6
  calculating one by one we get n=5
• 11 years agoHelpfull: Yes(11) No(0)
• holy shit...u guys solved it much easily....i got the ans but solved it dangerously...
  
  f1=1.6
  f2=(1+1)=f1*f1===2.56
  f3=(2+1)=f1*f2===4.1
  ..and so on... i found till f6
  ....then checked the sum....hence ans was 5
  p.s::: this took 4.30 min...so not bad... :)
  
• 11 years agoHelpfull: Yes(5) No(0)
• anjul meid please elaborate if this question can be done without the aid of calculator......logrithms involved for calculating n ...can these be done done without calculator
• 11 years agoHelpfull: Yes(2) No(1)
• @Ankita You have to use a calculator or log tables.
• 11 years agoHelpfull: Yes(1) No(0)
• here n=5.,it form a.p 1.6(1+2+3......+n)=24...solve it you got ans 5..without using calculator.
• 11 years agoHelpfull: Yes(1) No(5)