# At what rate per

Let rate = R % per annum

P = Rs.640

A = Rs.774.40

Time = 2 years

Now,

Amount (A) = P (1 + R/100)n [Where, A = Amount with compound interest

P = Present value

R = Annual interest rate

n = Time in years]

A = P (1 + R/100)2

774.40 = 640 (1 + R/100)2

(1 + R/100)2 = 774.40/640

(1 + R/100)2 = 1.21

(1 + R/100) = √(1.21)

R/100 = (1.1) - 1

R/100 = 0.1

R = 0.1 × 100

R = 10

Rate = 10% per annuam.

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