In a row of students, Bali is 7th from the left and Moti is 4th from the right. When they exchange their positions, Bali becomes 15th from the left. What will be the Moti’s new position from right?

Let the row have N students. Bali is 7th from the left, and Moti is 4th from the right, which means Moti is at position N-3 from the left. When they swap, Bali takes Moti's old place, and the question says Bali is then 15th from the left. So N-3 = 15, which gives N = 18.

Moti moves into Bali's old place, the 7th position from the left. Counting from the right, that is 18 - 7 + 1 = 12. So Moti is 12th from the right, and the answer is D.

• Core concept: position in a row seen from two ends. Position from the left plus position from the right equals N + 1, so once you know N, every position converts easily.
• Syllabus link: this is a basic reasoning item, but the same method of fixing the unknown total first applies to seating, ranking and calendar questions.
• Option A (Eighth) and B (Fourth) are just the numbers from the original data, not the new position.
• Option C (Eleventh) comes from using N = 18 but counting from the wrong end, or from a slip in the N-3 step.

Trap: people forget to first find the total number of students from the swap condition and try to answer with the wrong reference point.