Add a List into One Total

Supplied materials

• Paper and pencil; an adult may read aloud. No device, account or purchase is needed.

Learn the idea

A list holds several values in an order. An accumulator is a variable that collects a result across the list. To sum, begin with total = 0 and add each item exactly once. The current item changes from row to row; the total carries forward. These are different values.

Use list [3, 1, 4]. Algorithm: set total = 0; for each item in the list, set total = total + item; show total after the loop. Write one trace row for every item, including its position, item value and new total. The last item is 4, but the final sum is not just that item.

1. Write positions 1, 2, 3 beside values 3, 1, 4.
2. Start total = 0 in a separate start row.
3. Add the current item and record the total after each visit.
4. Compare the final total with 3 + 1 + 4.

Check your reasoning

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Take it further

Append 2 to the original list, giving [3, 1, 4, 2]. Expected totals: 3, 4, 8, 10; final total 10.

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