Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.

I need help with one.

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- Jul 3rd 2005, 12:20 PMHayabusaPlease help me solve this problem
Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.

I need help with one. - Jul 3rd 2005, 12:43 PMMathGuruDirect variation
**Suppose y varies directly as x and y=27 when x=3. Find x when y = 45.**

'Varies directly' most likely means an equation of the form y = x + k

Where k is a constant. So as x increases by some amount, y increases by that same amount.

change in y = change in x

y2 - y1 = x2 - x1

45 - 27 = x2 - 3

18 = x2 - 3

21 = x2

when y = 45,**x = 21** - Jul 3rd 2005, 12:47 PMHayabusa
Thank you so much I just forgot the formula then. :)

- Jul 3rd 2005, 01:41 PMticbol
Here is one way.

"y varies directly as x"

y ------> x

y = kx ----the equation.

y=27 when x=3

27 = k*3

k = 27/3 = 9

When y = 45,

45 = 9x

x = 45/9 = 5 ---answer.

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Another meaning of "y varies directly as x" is:

if x goes higher, then y goes higher too; if x goes lower, then y goes lower too....proportionately. - Jul 3rd 2005, 01:44 PMMathGuruVaries directly
Ticbol's answer may be more correct than mine.

It depends on what is meant by varies directly. - Jul 3rd 2005, 03:20 PMHayabusa
thanks again :D