RRB RPF RPSF SI and CONS Model Papers 10 with solutions

Question : 66 of 120

Marks: +1, -0

At what rate per cent per annum will the simple interest on a sum of money be

2/ 5

of the amount in 10 years ?

Solution:

(4) Let P be the principal and R% rate of interest.

∴{S.I.}= { {PR} × 10}/{100}= {\ {PR}}/{10}

According to the question,

{ {PR}}/{10}= (P+ { {PR}}/{10} ) ×{2}/{5}

⇒{ {R}}/{10}= (1+ { {R}}/{10} ) ×{2}/{5}

⇒{ {R}}/{10}= {2}/{5}+ { {R}}/{25}

⇒{R}/{10}- {R}/{25}= {2}/{5}

⇒{5 R-2 R}/{50}= {2}/{5}

⇒{3 R}/{50}= {2}/{5}

⇒ R= {50 ×2}/{3 ×5}= {20}/{3}=6 {2}/{3}

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