Find the weighted average of the numbers −3 and 5 with three fifths of the weight on the first number and two fifths on the second number.

4.8
1.8
0.2
−1.8

1 answer

To find the weighted average, we use the formula:

\[ \text{Weighted Average} = \frac{(w_1 \cdot x_1) + (w_2 \cdot x_2)}{w_1 + w_2} \]

where \(w_1\) is the weight on the first number, \(x_1\) is the first number, \(w_2\) is the weight on the second number, and \(x_2\) is the second number.

In this case:

  • \(x_1 = -3\)
  • \(x_2 = 5\)
  • \(w_1 = \frac{3}{5}\)
  • \(w_2 = \frac{2}{5}\)

Now, substitute the values into the formula:

\[ \text{Weighted Average} = \frac{\left(\frac{3}{5} \cdot (-3)\right) + \left(\frac{2}{5} \cdot 5\right)}{\frac{3}{5} + \frac{2}{5}} \]

Calculating the numerator:

\[ \frac{3}{5} \cdot (-3) = -\frac{9}{5} \]

\[ \frac{2}{5} \cdot 5 = \frac{10}{5} = 2 \]

Thus, the numerator becomes:

\[ -\frac{9}{5} + 2 = -\frac{9}{5} + \frac{10}{5} = \frac{1}{5} \]

Now, calculate the denominator:

\[ \frac{3}{5} + \frac{2}{5} = \frac{5}{5} = 1 \]

So, the weighted average is:

\[ \text{Weighted Average} = \frac{\frac{1}{5}}{1} = \frac{1}{5} = 0.2 \]

Therefore, the weighted average of the numbers -3 and 5 is 0.2.