In a row of 50 books, Book A is 15th from left and Book B is 20th from right. How many books lie between them?

Question

In a row of 50 books, Book A is 15th from left and Book B is 20th from right. How many books lie between them?

1. A. 17
2. B. 15 (Correct answer)
3. C. 12
4. D. 10

Correct Answer

Option B — 15

Detailed Solution & Explanation

The correct answer is 15.

Key Points

• Convert both positions to the same reference point. Book B is 20th from the right in a row of 50, so from the left it is 50 − 20 + 1 = 31st.
• Book A is 15th from the left.
• Books strictly between them: 31 − 15 − 1 = 15.

Additional Information

• The conversion formula is position from left = total − position from right + 1; the +1 is what people drop.
• *Between* excludes both books themselves, hence the second −1.
• A useful check: positions 16 to 30 inclusive is 15 books, matching the subtraction.

प्रश्न (हिन्दी में)

50 पुस्तकों की एक पंक्ति में, पुस्तक A बाएँ से 15वें स्थान पर है और पुस्तक B दाएँ से 20वें स्थान पर है। उनके बीच कितनी पुस्तकें हैं?

1. A. 17
2. B. 15
3. C. 12
4. D. 10