The amount doubles itself under Simple Interest in 2.5 years. In how many years will it become 45 times of itself?

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UP Police SI (दरोगा) Official PYP (Held On: 23 Nov 2021 Shift 1)
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  1. 115
  2. 120
  3. 110
  4. 105

Answer (Detailed Solution Below)

Option 3 : 110
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UP Police SI (दरोगा) Official PYP (Held On: 2 Dec 2021 Shift 1)
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Detailed Solution

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Given:

Under Simple Interest (SI), the amount doubles in 2.5 years.

Formula used:

Amount = Principal + Simple Interest

Simple Interest (SI) = Principal × Rate × Time / 100

Calculations:

When the amount doubles, SI = Principal.

⇒ Principal × Rate × Time / 100 = Principal

⇒ Rate × Time / 100 = 1

⇒ Rate × 2.5 = 100

⇒ Rate = 40%

To calculate the time for the amount to become 45 times of itself:

⇒ SI = Principal × (45 - 1)

⇒ Principal × Rate × Time / 100 = Principal × 44

⇒ Rate × Time / 100 = 44

⇒ 40 × Time / 100 = 44

⇒ Time = (44 × 100) / 40

⇒ Time = 110 years

∴ The correct answer is option (3).

Shortcut TrickLet the principal amount be P.

The amount doubles itself, meaning it becomes 2P.

Increases 2P - P = P

P increases in 2.5 years

And amount becomes 45 times

Increases 45P - P = 44P

So, 44P increases in (2.5 × 44) / 1 = 110 years.

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