can someone help me with the steps of this so I can understand it better?
If f(x) varies directly with x and f(x) = 2 when x = 10, then what is the value of f(x) when x = 40?
(Points : 4)
8
45
200
320

Question

can someone help me with the steps of this so I can understand it better? 
If f(x) varies directly with x and f(x) = 2 when x = 10, then what is the value of f(x) when x = 40? 
(Points : 4)
       8
       45
       200
       320

jim_thompson5910 · Answer

"f(x) varies directly with x" which means 

f(x) = k*x

where k is some constant

jim_thompson5910 · Answer

we are told that " f(x) = 2 when x = 10", so plug these two values in and then solve for k

f(x) = k*x

10 = k*2

10/2 = k

5 = k

k = 5

jim_thompson5910 · Answer

That means our equation goes from f(x) = k*x to f(x) = 5x

jim_thompson5910 · Answer

Do you see how to finish up?

anonymous · Answer

ok then would I divide f(x) to x to get the k?

jim_thompson5910 · Answer

exactly

jim_thompson5910 · Answer

once you figure out k, you plug in x = 40 into f(x) = 5x to get your final answer

anonymous · Answer

ok that makes sense

anonymous · Answer

thank you

jim_thompson5910 · Answer

sure thing