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---
id: 5e9a093a74c4063ca6f7c15d
title: Data Cleaning Introduction
challengeType: 11
videoId: ovYNhnltVxY
---
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# --description--
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*Instead of using notebooks.ai like it shows in the video, you can use Google Colab instead.*
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More resources:
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- [Notebooks on GitHub ](https://github.com/ine-rmotr-curriculum/data-cleaning-rmotr-freecodecamp )
- [How to open Notebooks from GitHub using Google Colab. ](https://colab.research.google.com/github/googlecolab/colabtools/blob/master/notebooks/colab-github-demo.ipynb )
# --question--
## --text--
What will the following code print out?
```py
import pandas as pd
import numpy as np
s = pd.Series(['a', 3, np.nan, 1, np.nan])
print(s.notnull().sum())
```
## --answers--
3
---
```
0 True
1 True
2 False
3 True
4 False
dtype: bool
```
---
```
0 False
1 False
2 True
3 False
4 True
dtype: bool
```
## --video-solution--
1