Predict the result
What does a sum from i equals one to five of two i mean?
How many terms will you add?

Set up the model
The limits select the integers one through five.
Substitute each of those integers into two i.

Work the example
The five terms are two, four, six, eight, and ten.
Add every selected term once.
The sum is thirty.
There are five terms, including both endpoints.

Check the result
Now sum three i from i equals one through five.
Take eight seconds to think before the answer appears.
[Eight-second silent pause to work; the answer remains hidden.]
The terms are three, six, nine, twelve, and fifteen.
Their sum is forty-five.

Interpret the result
The limits and the expression together define the sum.
Use the original task and check that your result fits its meaning.