Question

Suppose f(x) varies inversely with x and f(x)=3 when x=10. What is the value of f(x) when x=15

Answer 1

The answer to this question would be: C=4.5
Assuming the function consist of f(x)= ax function, then for x=10 and f(x)=3 you can determine the variable a
f(x)= ax
3= a*10
a= 3/10= 0.3

Then the function must be f(x)= 0.3x
For x= 15, the f(x) would be:
f(x)= 0.3x
f(15)= 0.3 * 15= 4.5

Answer 2

Answer:- C is the right answer, f(x)=4.5 when x=15.

Explanation:-

Given:-f(x) varies inversely with x and f(x)=3 when x=10.

Using direct proportion to find the value of f(x) when x=15

We have, $\frac{x_1}{f(y_1)}=\frac{x_2}{f(y_2)}\\\\\Rightarrow\frac{10}{3}=\frac{15}{f(x)}\\\\\Rightarrow\ f(x)=\frac{15\times3}{10}\\\\\Rightarrow\ f(x)=\frac{45}{10}\\\\\Rightarrow\ f(x)=4.5$

Thus C is the right answer, f(x)=4.5 when x=15.