Multiple choice

7 years ago , the ages ( in years ) of A and B were in the ratio 4 : 5 and 7 years hence they will be in the ratio 5 : 6 . The present age of B is : 7 वर्ष पहले A और B की आयु का अनुपात 4 : 5 था . और 7 वर्ष बाद उनकी आयु का अनुपात 5 : 6 हो जाता है तो B की वर्तमान आयु क्या है ?

  1. 56 years / वर्ष

  2. 63 years / वर्ष

  3. 70 years / वर्ष

  4. 77 years / वर्ष
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D Correct answer
Explanation

Let present ages be A and B. 7 years ago: (A-7)/(B-7) = 4/5, so 5A-35 = 4B-28, or 5A-4B = 7. 7 years hence: (A+7)/(B+7) = 5/6, so 6A+42 = 5B+35, or 6A-5B = -7. Solving these equations: from first, A = (4B+7)/5. Substituting in second: 6(4B+7)/5 - 5B = -7. This gives B = 77 years.

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