What is #x# when #y=18#, if #y=5# when #x=4#?

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Answer 1 · 2016-11-14T08:58:22

The question is quite incomplete, There may be several answers for it.

For example.,

Lets say # y = x + 1 # is equation 1.
So here, when #x = 4, y = 5.#

Also, # y = 1.25 x #, is equation 2

Here also, when #x= 4 , y# = 5 ,

But these equations give different results when #y# = 18

For equation 1,

#18 = x + 1#
So, #x = 17#

For equation 2,

#18 = 1.25x#

#18/1.25 = x#

So, #x = 14.4#

Answer 2 · 2016-11-14T09:24:38

Some rule or formula needs to be given to connect x and y.

In addition to what has been given by Anuj, here are other options for x and y if they are in proportion to each other:

Directly proportional:

# x/18 = 4/5#

#5x = 4xx18#

#x = (4xx18)/5#

#x = 14.4#

Inversely proportional:

#x xx y = 5xx4 = 20#

#x xx 18 =20#

#x = 20/18 = 10/9#

If they are not in proportion, some rule or formula needs to be given to connect x and y.