The average of present ages of five persons is 29.2. Among them, the sum of the present age of a girl and brother including her teacher is 11 years more than the average of the present ages of her parents. Find the sum of the present age of the girl and her teacher if it is given that her brother will be of 22 years after 5 years.
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40 years
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41 years
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39 years
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45 years
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Cannot be determined
C
Correct answer
Explanation
Total age of 5 persons = 5 × 29.2 = 146 years. Brother's current age = 22 - 5 = 17 years. Given: girl + brother + teacher = parents' average + 11. Parents' average = (146 - girl - brother - teacher)/2. So girl + 17 + teacher = (146 - girl - 17 - teacher)/2 + 11. Let g = girl + teacher. Then g + 17 = (129 - g)/2 + 11, so 2g + 34 = 129 - g + 22, giving 3g = 117, so g = 39.