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Mathematics

A number of two digits exceeds four times the sum of its digits by 6 and it is increased by 9 on reversing the digits. Find the number.

Linear Equations

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Answer

Let's consider the digits at ten's place as x and let the digit at unit's place be y.

Number = 10 × x + y = 10x + y,

On reversing digits the number is = 10 × y + x = 10y + x.

According to first condition, we have

⇒ 10x + y - [4(x + y)] = 6

⇒ 10x + y - 4x - 4y = 6

⇒ 10x - 4x + y - 4y = 6

⇒ 6x - 3y = 6

⇒ 2x - y = 2 ……(i)

According to second condition, we have

⇒ 10x + y + 9 = 10y + x

⇒ 10x - x + y - 10y = -9

⇒ 9x - 9y = -9

⇒ x - y = -1

⇒ y - x = 1 ……(ii)

Adding eq. (i) and (ii) we get,

⇒ 2x - y + (y - x) = 2 + 1

⇒ x = 3.

Substituting value of x in (ii) we get,

⇒ y - 3 = 1

⇒ y = 4.

Number = 10 × x + y = 10 × 3 + 4 = 30 + 4 = 34.

Hence, number = 34.

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