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Option 3 : 25%

As not mentioned we assume that interest is compounded annually so n = 1.

After 2 years,

S.I. = prt = 2pr

C.I. = p(1 + r/n)nt – p = p(1 + r)2 – p = p(2r + r2)

C.I. – S.I. = pr2

After 3 years,

S.I. = prt = 3pr

C.I. = p(1 + r / n)nt – p = p(1 + r)3 – p = p(r3 + 3r2 + 3r)

C.I. – S.I. = p(r3 + 3r2)

Ratio = r2 / (r3 + 3r2) = 4 / 13

⇒ 13r2 = 4r3 + 12r2

⇒ r2 = 4r3

⇒ r = 1 / 4 = 25%

∴ rate of interest is 25%.

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