Proportion Calculation: Finding x

The given problem presents a proportion: $2.8 : 3.8 : : x : 5.7$

This notation means the ratio of the first two numbers is equal to the ratio of the last two numbers. We can write this as an equation:

$ \frac{2.8}{3.8} = \frac{x}{5.7} $

Solving for x

To find the value of x, we need to rearrange the equation.

1. Isolate x by multiplying both sides of the equation by $5.7$:

   $ x = \frac{2.8}{3.8} \times 5.7 $

2. Perform the calculation:

   $ x = \frac{2.8 \times 5.7}{3.8} $

   $ x = \frac{15.96}{3.8} $

   $ x = 4.2 $

Therefore, the number in the place of x is $4.2$.