Q. On a chess board, in how many different ways can 6 consecutive squares be chosen on the diagonals along a straight path ?
(a) 4
(b) 6
(c) 8
(d) 12
Correct Answer: (b) 6
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Chess Board Consecutive Squares Chosen
Given:
– Chess board has 2 diagonals with 8 squares each
– Need to select 6 consecutive squares
– These 6 squares must be consecutive along a diagonal
Step 1: Analyze one diagonal
– Diagonal has 8 squares
– Need to select 6 consecutive squares
– Think of 6 squares as one block
– This block can slide along diagonal
Step 2: Calculate possible positions on first diagonal
– 8 squares total, need 6 consecutive
– First position: squares 1-6
– Second position: squares 2-7
– Third position: squares 3-8
Total positions on first diagonal = 3
Step 3: Calculate possible positions on second diagonal
– Same calculation as first diagonal
– 3 possible positions
Total positions on second diagonal = 3
Step 4: Calculate total number of ways
– First diagonal: 3 ways
– Second diagonal: 3 ways
Total ways = 3 + 3 = 6