Challenge Level

Find the sum of all the dates in a week (you could use the dates of this week).

Write down the total.

Multiply the number of the first day in the week by $7$.

Add $21$ to the product.

Write down the total.

What do you notice about the two results?

Can you explain what accounts for the second answer?

Choose two consecutive weeks on the calendar and find the sum of the dates.

Multiply the number of the first day in the first week by $14$.

Add $91$ to the product.

How does this compare with using just one week?

Why do you multiply by $14$ and why add $91$?