A letter is known to have come from either TATANAGAR or CALCUTTA. On the envelope, only two consecutive letters 'TA' are visible. The probability that the letter came from TATANAGAR is:

A letter is known to have come from either TATANAGAR or CALCUTTA. On the envelope, only two consecutive letters 'TA' are visible. The probability that the letter came from TATANAGAR is:

• A. 7/11
• B. 4/11
• C. 2/9
• D. 1/2

Answer: A) 7/11

Explanation: TATANAGAR has 8 pairs, 'TA' appears twice (prob 2/8 = 1/4). CALCUTTA has 7 pairs, 'TA' appears once (prob 1/7). P(TATA|TA) = (1/2 × 1/4) / [(1/2 × 1/4) + (1/2 × 1/7)] = (1/4) / (1/4 + 1/7) = 7/11.