SSC CGL 2024 PYQ — Question 58

SSC CGL - 12 Sep 2024 - Shift 2 • Quantitative Aptitude • Q58

For the following equations, what are the values of a and b to have infinitely many solutions?

ax + by = 2

3x - (5 - 2a)y = 6

Show answer & explanation

Correct answer: C

Explanation

The correct answer is option 3 i.e. a = 1,b = - 1.

Condition for infinitely many solutions is: If there are two equations, say;

a1x + b1y = c1 and a2x + b2y = c2

Then, a1a2=b1b2=c1c2{a_1 \over a_2} = {b_1 \over b_2} = {c_1 \over c_2}

According to the given question, the two equations are:

ax + by = 2

3x - (5 - 2a)y = 6

⇒ a3=26{a \over 3} = {2 \over 6}

⇒ 6a = 6

⇒ a = 1

Now, b−(5−2a)=26{b \over -(5 - 2a)} = {2 \over 6}

⇒ 6b = -2(5 - 2)

⇒ 6b = -6

⇒ b = -1

Hence the values of a and b to have infinitely many solutions are a = 1,b = - 1.