Understanding the Problem
We have data about downloads of a mobile app 'A' over two years:
1. 2014:
- Total downloads: 200
- Percentage on Android: 60\%
2. 2015:
- Total downloads: 600
- Percentage on Android: 40\%

Question: What was the percent change from 2014 to 2015 in the number of downloads on the Android platform for the app 'A'?

Breaking Down the Problem
First, let's find out how many Android downloads there were in each year.

Calculating Android Downloads in 2014
- Total downloads in 2014: 200
- Percentage on Android: 60\%

Number of Android downloads in 2014:

$$
\(\text { Android }_{2014}=60 \% \times 200=0.60 \times 200=120\)
$$


Calculating Android Downloads in 2015
- Total downloads in 2015: 600
- Percentage on Android: $40 \%$

Number of Android downloads in 2015:

$$
\(\text { Android }_{2015}=40 \% \times 600=0.40 \times 600=240\)
$$


Determining the Change in Android Downloads
Now, we have:
- Android downloads in 2014: 120
- Android downloads in 2015: 240

The increase in Android downloads from 2014 to 2015:

$$
\(\text { Increase }=\text { Android }_{2015}-\text { Android }_{2014}=240-120=120\)
$$


Calculating the Percent Change

The percent change is calculated using the formula:

$$
\(\text { Percent Change }=\left(\frac{\text { New Value }- \text { Old Value }}{\text { Old Value }}\right) \times 100 \%\)
$$


Plugging in the numbers:

$$
\(\text { Percent Change }=\left(\frac{240-120}{120}\right) \times 100 \%=\left(\frac{120}{120}\right) \times 100 \%=1 \times 100 \%=100 \%\)
$$


Verifying the Calculation

Let me double-check the calculations to ensure no mistakes were made.
1. Android downloads in 2014:
- 60\% of 200:

$$
\(-0.60 \times 200=120\)
$$

2. Android downloads in 2015:
- $40 \%$ of 600:

$$
\(-0.40 \times 600=240\)
$$

3. Increase:
- $\(240-120=120\)$ :
4. Percent change:
- $\(\frac{120}{120} \times 100 \%=100 \%\)$

Everything checks out!