Start with the numbers from $0$ - $20$:

Can you arrange these numbers into seven sets of three numbers, so that the totals of the sets are consecutive?

For example, one set might be $\{2, 7, 16\}$

$2 + 7 + 16 = 25$

another might be $\{4, 5, 17\}$

$4 + 5 + 17 = 26$

As $25$ and $26$ are consecutive numbers these sets might be part of your solution.

Once you've found a solution, here are some questions you might like to consider:

• Is there more than one possible set of seven consecutive totals? How do you know?
• Is there more than one way to make the seven totals?
• Could you make seven sets that all had the same total?
• Could you make seven sets whose totals went up in twos? Or threes? Or...