A number is first decreased by 20% and then increased by 15%. The number so obtained is 64 less than the original number. The original number is:

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  1. 700
  2. 800
  3. 850
  4. 600

Answer (Detailed Solution Below)

Option 2 : 800
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Detailed Solution

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Given:

A number is first decreased by 20% and then increased by 15%.

The number so obtained is 64 less than the original number

Calculations:

Let the number be 100x

Number after decrement of 20% = 100x × (100 - 20)/100

100x × 80/100 = 80x 

Number after 15% increment = 80x × (100 + 15)/100

⇒ 80x × (100 + 15)/100 = 92x

According to the question

100x - 92x = 64  (difference of the original and new number)

⇒ 8x = 64

⇒ x = 8

Original number = 100x = 800 

∴ The correct choice is option 2.

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