Question

The difference between compound interest and simple interest on a sum of 3,000 for 3 years is 93. The rate per cent per annum is​

Answer 1

Answer:10%

Step-by-step explanation:

Let Interest be I    

  Principle= P=3000, time =t=3 and rate of interest=r

Then  for C I=P(1+r)³-P =3000(1+r)³-3000

For simple interest S I= P*r*t= 3000*3*r

we have 3000(1+r)³-3000- 9000r=93

        ⇒ 3000+3000r³+9000r²+9000r-3000-9000r=93

        ⇒ 3000r³+9000r²-93=0

        ⇒ 3000r³ -300r²+9300r²-93=0

        ⇒ 300r²(10r-1)+93(100r²-1)=0

        ⇒ 300r²(10r-1)+93 (10r+1)(10r-1)=0

        ⇒ (10r-1)(300r²-930r-93)=0

      solving  we have 10r-1=0 or r=1/10=10%

Hence interest rate is 10%

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Answer 2

Answer:

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