## Determination of the unknown term of a ratio

Examples:

- Determine the value of x in proportion:

Solution:*5 x = 8. 15**(applying the fundamental property)**5 x = 120**x = 24*

Therefore, the value of*x*é 24.

- Determine the value of x in proportion:

Solution:*5 (x-3) = 4. (2x + 1)**(applying the fundamental property)**5x - 15 = 8x + 4**5x - 8x = 4 + 15**-3x = 19**3x = -19**x =*

Therefore, the value of*x*é .

- The numbers 5, 8, 35 and x, in that order, form a proportion. Determine the value of x.

Solution:

*(applying the fundamental property)**5 x = 8. 35*

5x = 280*x = 56*

Therefore, the value of*x*é 56.

## Problem solving involving proportions

Example:

- In a saline of each cubic meter (m
^{3}) of salt water, 40 dm^{3}of salt To get 2 m^{3}salt, how many cubic meters of salt water are needed?**Solution:**

The amount of salt removed is**proportional**to the volume of salt water. We indicate by x the amount of salt water to be determined and set the proportion:

Remember that 40dm^{3}= 0.04m^{3}.

*(applying the fundamental property)**1 . 2 = 0.04. x*

0.04x = 2*x = 50 m*^{3}

So it takes 50 m^{3}of salt water.