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BBA-DBE Bangalore 2025 PYQsQuantitative Ability. Free, no login required.

If x−2y+4z=6x - 2y + 4z = 6, 3x+y+5z=43x + y + 5z = 4 and 2x−y+3z=42x - y + 3z = 4, then what is the value of (2x–3y+5z)(2x – 3y + 5z)?

Solution

✅ Correct Option: 3

Given the system of equations:

(1) x−2y+4z=6x - 2y + 4z = 6

(2) 3x+y+5z=43x + y + 5z = 4

(3) 2x−y+3z=42x - y + 3z = 4

Add (2) and (3):

(3x+y+5z)+(2x−y+3z)=4+4(3x+y+5z) + (2x-y+3z) = 4+4

5x+8z=85x + 8z = 8 (Equation A)

Multiply (3) by 2: 4x−2y+6z=84x - 2y + 6z = 8 (Equation 3')

Subtract (1) from (3'):

(4x−2y+6z)−(x−2y+4z)=8−6(4x - 2y + 6z) - (x - 2y + 4z) = 8 - 6

3x+2z=23x + 2z = 2 (Equation B)

From (B), 2z=2−3x2z = 2 - 3x. Substitute this into (A):

5x+4(2z)=85x + 4(2z) = 8

5x+4(2−3x)=85x + 4(2 - 3x) = 8

5x+8−12x=85x + 8 - 12x = 8

−7x=0⇒x=0-7x = 0 \Rightarrow x = 0

Substitute x=0x=0 into (B): 3(0)+2z=2⇒2z=2⇒z=13(0) + 2z = 2 \Rightarrow 2z = 2 \Rightarrow z = 1.

Substitute x=0x=0 and z=1z=1 into (2):

3(0)+y+5(1)=43(0) + y + 5(1) = 4

y+5=4⇒y=−1y + 5 = 4 \Rightarrow y = -1.

Now, calculate 2x−3y+5z2x - 3y + 5z:

2(0)−3(−1)+5(1)=0+3+5=82(0) - 3(-1) + 5(1) = 0 + 3 + 5 = 8.

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