RRB Assistant Loco Pilot and Technician Model Paper 3 with solutions

Question : 22 of 100

Marks: +1, -0

A sum of money placed at compound interest double itself at 2 years. The year it will take to amount 4 times itself is

Solution:

(b) Let the sum be ₹1 which becomes ₹ 2 after 2 years
⇒

2 = ( 1 + { { R } } /{ 100 } ) ^ { 2 }

...(i)
Let the sum of ₹1 becomes ₹4 after 'n' years
⇒

4 = 1 ( 1 + { { R } } { 100 } ) ^ { { n } }

⇒

2 ^ { 2 } = 1 ( 1 + { { R } }/ { 100 } ) ^ { { n } }

⇒

[ 1 ( 1 + { { R } }/ { 100 } ) ^ { 2 } ] ^ { 2 }

( 1 + { { R } } /{ 100 } ) ^ { {n } }

⇒ n = 4 years

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