A homeowner installs \(28\) solar panels. Type A panels produce \(320\,\text{W}\) each, and Type B panels produce \(400\,\text{W}\) each. Together, the panels produce \(10\,\text{kW}\).
a) How many panels of each type are installed?
b) The system output will be increased to \(12\,\text{kW}\). How many additional Type B panels are needed if the number of Type A panels stays the same?
Use the distributive property before isolating the variable. Your response must show the equation immediately before and immediately after distribution.
Hints
- Convert all power values to watts.
- Use one variable for the number of one panel type.
- The two panel counts add to \(28\).
- In part b, keep the Type A count unchanged and recalculate the required Type B output.
Solution
1. Convert \(10\,\text{kW}\) to \(10{,}000\,\text{W}\). Let \(x\) be the number of Type A panels, so \(28-x\) are Type B panels.
2. Solve \(320x+400(28-x)=10{,}000\). This simplifies to \(-80x=-1200\), so \(x=15\). Therefore, there are \(15\) Type A panels and \(13\) Type B panels.
3. The \(15\) Type A panels produce \(15\cdot320=4800\,\text{W}\).
4. To reach \(12{,}000\,\text{W}\), Type B panels must produce \(12{,}000-4800=7200\,\text{W}\), requiring \(7200\div400=18\) Type B panels.
5. Since \(13\) Type B panels are already installed, \(18-13=5\) additional Type B panels are needed.
Answer
a) Before distribution: \(320x+400(28-x)=10{,}000\). After distribution: \(320x+11{,}200-400x=10{,}000\). There are \(15\) Type A panels and \(13\) Type B panels.
b) \(5\) additional Type B panels are needed.