CA Foundation · Quantitative Aptitude · Equations
If one root of the equation x² − 9x + k = 0 is 4, what is the value of the other root?
The other root is 5. For x² − 9x + k = 0 the sum of the roots equals 9, so with one root equal to 4 the second root is 9 − 4 = 5. This also gives k = 20, which factorises correctly.
- A4
- B5Correct
- C−5
- D13
Explanation
The sum of the roots is 9 (from −b/a). If one root is 4, the other is 9 − 4 = 5. Check: k = 4 × 5 = 20, and x² − 9x + 20 = (x − 4)(x − 5). Option 13 comes from adding 4 to 9 instead of subtracting.
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