PL-300 Visualize and analyze the data Practice Question
A Power BI report includes a bar chart showing total sales by product category. The report designer wants to add a trend line to the chart to show the overall sales trend over time. Which type of visual should be used instead?
⚠ Common exam trap
Many candidates think a bar chart with a trend line added via the analytics pane is acceptable, but the question asks which visual should be used instead, implying the bar chart is not the optimal choice for showing a trend over time.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Line chart
A line chart is the correct visual to show a trend over time because it plots data points connected by straight lines, making it easy to see the overall direction and pattern of total sales across a continuous time axis. Bar charts, including stacked variants, are designed for comparing discrete categories, not for displaying continuous trends.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Stacked bar chart
Why it's wrong here
A stacked bar chart aggregates categorical data into segments, treating time as discrete labels rather than a continuous scale. Trend lines require a continuous, ordered axis with evenly spaced time intervals to fit a regression or moving average; stacked bars break that continuity, making a meaningful trend line impossible. Additionally, the stacking mechanism shifts each segment's baseline, so tracking a single series' trajectory over time becomes visually misleading and analytically unsound.
- ✓
Line chart
Why this is correct
A line chart encodes data points along a continuous time axis and connects them with straight lines, allowing the eye to perceive direction, rate of change, and periodicity. Because the x-axis is continuous and time-ordered, Power BI can compute and overlay a trend line using linear regression, moving average, or other built-in analytics in the Analytics pane. It is the default and recommended visual for time-series trend analysis because it preserves the sequential structure of the data.
- ✗
Scatter chart
Why it's wrong here
A scatter chart plots two numeric measures on the X and Y axes to reveal correlation or distribution, with each point representing an observation of those two variables. If time is placed on the x-axis, points would be spaced according to date values, but without connecting lines, sequence and direction are difficult to discern; the built-in trend line on a scatter chart performs a regression between the two numeric fields, not a time-series smoothing. Scatter charts are optimized for relationship analysis, not for showing how a single measure evolves over time.
- ✗
Pie chart
Why it's wrong here
A pie chart represents a single data series as slices of a circle, showing the proportion each category contributes to the total at a single point in time. It has no x-axis or continuous time dimension, and its visual encoding—angle and area—is designed for part-to-whole comparisons, not for tracking change. You cannot plot multiple time periods meaningfully on the same pie chart, and a trend line cannot be added because there is no continuous numeric axis to fit a regression or smoothing line.
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