Question

If one term of a proportion is not known, what can be used to find the value of that term?]
a.

substitution

c.

cross-multiplication
b.

graphing

d.

adding all the numbers together

Answer 1

c. cross multiplication
For eg. let x be the unknown number,
5:x::5:7
5/x=5/7
when cross multiplying you will get,
7*5=5*x
35=5x
x=35/5
x=7

Answer 2

Answer:

The value of the unknown proportion can be find out only by using cross multiplication method.

Solution:

Let the proportion be $4: x:: 20:40$ and consider the unknown proportion as x.

1. Substitution

We need to know the value in order to substitute it in the place of the unknown proportion  

$4: x::20:40$

2. Cross-multiplication

$\begin{array} { l } { 4 : \mathrm { x } : : 20 : 40 } \\\\ { \frac { 4 } { \mathrm { x } } = \frac { 20 } { 40 } } \\\\ { 20 \mathrm { x } = 160 } \\\\ { x = 8 } \end{array}$

Thus, the value of the unknown proportion x is 8.

3. Graphing

Through graphing, we cant able to find the value of x (unknown proportion).

4. Adding all the numbers together

We cannot find the number x by adding the values together.

$4: x::20:40$

Thus, we can find out the unknown proportion x only by cross multiplication.