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‘x’ varies directly with the cube of ‘y’, and inversely with the square of ‘z’. If x = 1/36 when y = 2 and z = 3, then what is the value of 800x when
Question

‘x’ varies directly with the cube of ‘y’, and inversely with the square of ‘z’. If x = 1/36 when y = 2 and z = 3, then what is the value of 800x when y = 3 and z = 5?

A.

9/800

B.

27

C.

800/9

D.

9

Correct option is B

Given:
x varies directly with the cube of y, and inversely with the square of z.
x =136 \frac{1}{36}​ when y = 2 and z = 3.
To find 800x when y = 3 and z = 5.
Solution:
According to the question:
x varies directly with y3y^3​ and inversely with z2z^2​:
x = k×y3z2k \times \frac{y^3}{z^2}​​
where k is a constant.
Now:
Substituting the values;

136=k×2332\frac{1}{36} = k \times \frac{2^3}{3^2}​​

136=k×89\frac{1}{36} = k \times \frac{8}{9}​​

936=8k\frac{9}{36} = 8k​​

14=8k\frac{1}{4} = 8k​​

k=132k = \frac{1}{32}​​

Now,
Substitute the values y = 3 and z = 5 into the formula for x:

x=132×3352x = \frac{1}{32} \times \frac{3^3}{5^2}​​

x=132×2725x = \frac{1}{32} \times \frac{27}{25}​​

x=27800x = \frac{27}{800}​​

800x = 27
So, the value of 800x is 27.

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