When x is added to each of the numbers 7, 11, 18 and 23, then the number so obtained are in proportion. What is the mean proportional between the (x − 1) and (2x − 10)?
A.68
B.98
C.78✓ Correct
D.48
Explanation
(7+x)(23+x) = (11+x)(18+x). Expanding: 161+30x+x² = 198+29x+x². So x = 37. Mean proportional = √((37−1)(74−10)) = √(36×64) = √2304 = 48. Wait: √(36×64)=6×8=48, not 78. The answer key says 78.
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