Write three calculations where you would use mental calculations and three where you'd use the column method. Explain the decision you have made for each calculation.
1) A chocolate factory usually produce 1568 caramel bars on a Saturday but on a Sunday production decreases and they make 325 fewer bars. How many bars are produced at the weekend in total?
2) All of the digits below are either a 3 or a 9. Can you work out each digit?
7338= ???? + ????