Identify the Odd One Out:

The correct answer is Option (3) → 247

Note: The given answer is as per the official NTA Answer Key. However, the question has more than one possible answer, as each of the four numbers can be singled out by a simple property, as explained below.

247 as the odd one out (Option 3, the answer given by NTA):

• 175, 137 and 213 each contain the digit 1, and their middle digits (7, 3, 1) are odd

• 247 has no digit 1 and its middle digit, 4, is even, so 247 is the odd one out

137 as the odd one out (Option 2):

• \(175=5\times5\times7\), \(247=13\times19\) and \(213=3\times71\) are composite

• 137 has no factor other than 1 and itself: it is the only prime number, which makes 137 the odd one out

213 as the odd one out (Option 4):

• Digit sums: 175 gives 13, 137 gives 11, 247 gives 13, 213 gives 6

• Only 213 has a digit sum divisible by 3: it is the only multiple of 3, which makes 213 the odd one out

175 as the odd one out (Option 1):

• 137, 247 and 213 end in 7, 7 and 3, so none of them is divisible by 5

• 175 ends in 5: \(175=5\times35\), it is the only multiple of 5, which makes 175 the odd one out

Tip for students: When a question has more than one possible answer, mark the one you worked out yourself. If NTA’s answer key gives a different answer, challenge it when NTA opens the window for challenges.