Question 15

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Jambmaths question: 

U is inversely proportional to the cube of V and U = 81 when V = 2. Find U when V=3

Option A: 

24

Option B: 

27

Option C: 

32

Option D: 

36

Jamb Maths Solution: 

$\begin{align}  & U\propto \frac{1}{{{V}^{3}}} \\ & U=\frac{K}{{{V}^{3}}} \\ & \text{When }V=2,\text{ }U=81 \\ & 81=\frac{K}{{{2}^{3}}} \\ & K=81\times 8=648 \\ & \text{When }V=3,\text{ }U=? \\ & U=\frac{648}{{{3}^{3}}}=\frac{648}{27}=24 \\\end{align}$

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