We are learning to use the strategy work backwards. We used ourselves to solve the picnic problem. 75 people went on picnic. 20 had veggie burgers, 32 had sausages and we didn’t know how many people had beef burgers.
We sat in rows for which lunch we had had – roast beef, packed lunch, and soup. The row that had had baked potato sat down. They were the mystery number that we needed to find.
There were 15 of us. We took away the one packed lunch = 14
We took away the 4 soups = 10
We took away the 6 beef burgers = 4
We found the mystery number 4

For the picnic problem some pairs added the veggie burgers and sausages 20 + 32 = 52 then counted up to 75 to find the mystery number.