unimportant change maybe..

[angdrico]

As this is a learning for beginners, I think it is quite good for our learning.

they will write the table name in the code in 3 possible ways:

1. Their memory of the column name at sales.head()
2. Looking at the sales.head()
3. Looking at the h3 above it ("What's the mean of Costumers_Age?")

The code won't run if they misremember it, or don't look correctly at the sales.head(), or refer to the h3

Then they will try to solve it. After they stuck/found it/looking for a solution below, at least they got that message :) Or maybe just correct the h3, but maybe it's not better in terms of learning..