How to resolve propotion?

[Fokin]

How to resolove that proportion , i've tried picking numbers but is unsuccessfull^

If w, x, y and z are positive and w/x=y/z, which of the following is not always true ?

a)wz=xy

b) x/w=z/y

c)x/y=z/w

d)(w+x)/z=(y+z)/z

e) (x+w)/w=(z+y)/y

Right answer - C

[tpr-becky]

I think you mistyped the problem if the actual problem is w/x=y/z then the problem makes sense. You can pick numbers as you suggested but you can also manipulate the equation by cross multiplying

a) this is obtained by multiplying both sides by x and then by z (w=(y)(x)/z turns inot wz=yx)
b) if you use the equation from ( a) you can divide by w and then divide by y: (z=yx/w turns into z/y=x/w)
c) you cannot manipulate the equation to get this answer
e) this simplifies to x/w+1=z/y+1 which further simplifies to x/w=z/y (the same equation as in b)

[eaakbari]

a) Cross multiply
b) reciprocal
c) Aha!
d)Componendo
e) Reciprocal and then Componendo


Hence answer C

Note
Compnendo is
If a/b = c/d
then
(a+b)/b = (c+d)/d
HTH

[eaakbari]

As a side note, Post your question in the correct forum, this question belongs in PS

[ajith]

As a side note, Post your question in the correct forum, this question belongs in PS

Moved to PS Forum