When 30% of one number is subtracted from another number, the second number reduces to its four-fifths. What is the ratio of the first to the second number?

A 3 : 2

B 2 : 3

C 2 : 5

D 4 : 7

Solution

Correct Answer: Option B

Let,
the first and second numbers be x and y,

ATQ,
y - 30% of x = y (4/5)
⇒ y - (30x/100) = 4y/5
⇒ y - (3x/10) = 4y/5
⇒ (10y - 3x)/10 = 4y/5
⇒ (10y - 3x)/2 = 4y
⇒ 10y - 3x = 8y
⇒ - 3x = 8y - 10y
⇒ 3x = 2y
⇒ x/y = 2/3
∴ x : y = 2 : 3

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