Question
Download Solution PDFIf x is the mean proportional between 12.8 and 64.8 and y is the third proportional to 38.4 and 57.6, then 2x : y is equal to:
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFIf x is the mean proportional between 12.8 and 64.8, then
12.8 : x : : x : 64.8
⇒ 12.8/x = x/64.8
⇒ x2 = 12.8 × 64.8
⇒ x = √[16 × 0.8 × 0.8 × 81]
⇒ x = 4 × 0.8 × 9
If y is the third proportional to 38.4 and 57.6, then
38.4 : 57.6 : : 57.6 : y
⇒ 38.4/57.6 = 57.6/y
⇒ y = (57.6 × 57.6)/38.4
⇒ y = 86.4
Now,
2x : y = 2 × 4 × 0.8 × 9 : 86.4 = 2 : 3
Short Trick :
Mean Proportional x = √12.8 × 64.8 = 28.8
Third proportional y = (57.6 × 57.6)/38.4 = 86.4
Now,
2x : y = 2 × 28.8 : 86.4 = 2 : 3Last updated on Jul 16, 2025
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