एक सीढ़ी में सबसे नीचे (45) ईंटें हैं और हर ऊपर वाली पंक्ति में (3) ईंटें कम हैं। (12) पंक्तियों में कुल कितनी ईंटें होंगी?
A stair pattern has (45) bricks in the bottom row and (3) fewer bricks in each upper row. How many bricks are there in (12) rows?
Explanation opens after your attempt
C. (342)
Concept
This is the AP \(45,42,39,\ldots\), and (S_{12}=6[90+11(-3)]=342). Exam tip: treat the decrease as a negative common difference.
Why this answer is correct
The correct answer is C. (342). This is the AP \(45,42,39,\ldots\), and (S_{12}=6[90+11(-3)]=342). Exam tip: treat the decrease as a negative common difference.
Exam Tip
यह \(45,42,39,\ldots\) श्रेणी है और (S_{12}=6[90+11(-3)]=342)। परीक्षा में कमी को ऋणात्मक सार्व अंतर मानें।
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