Question:medium

Let a and b be natural numbers. If \(a^2+ab+a=14\) and \(b^2+ab+b=28\), then (2a+b) equals

Updated On: Jul 4, 2026
  • 7

  • 10

  • 9

  • 8

Show Solution

The Correct Option is D

Solution and Explanation

To resolve the problem, we must determine the values of \(a\) and \(b\) that fulfill the provided equations and subsequently calculate \(2a+b\).

The given equations are:

\(a^2+ab+a=14\) (Equation 1)

\(b^2+ab+b=28\) (Equation 2) 

Rearranging Equation 1 yields:

\[a(a+b+1)=14\]

Given that \(a\) is a natural number, and the factors of 14 are 1, 2, 7, and 14, we examine each possibility:

1. If \(a=1\), then \(1(b+2)=14\), implying \(b+2=14\), thus \(b=12\).

2. If \(a=2\), then \(2(b+3)=14\), implying \(b+3=7\), thus \(b=4\).

3. If \(a=7\), then \(7(b+8)=14\), which is not feasible for a natural number \(b\).

4. If \(a=14\), then \(14(b+15)=14\), which is not feasible as \(b+15\) cannot equal 1.

We now verify these potential solutions by substituting them into Equation 2:

Substituting \(a=2\) and \(b=4\) into Equation 2:

\[b^2+ab+b=28\]

\[4^2+2\times4+4=16+8+4=28\]

This pair of values satisfies both equations; therefore, \(a=2\) and \(b=4\).

Finally, we compute \(2a+b\):

\[2a+b=2(2)+4=4+4=8\]

The result is 8.

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