This activity will engage students. They choose the numbers but their teacher is able to tell them their final total. How?
Choose one child to pick out 3 consecutive numbers and write them on a whiteboard to show the rest of the class. Another child can choose a multiple of 3 which he tells the teacher.
The whole class can then follow the instructions individually on paper. This is good practice for long multiplication.
Choose a child to reveal the final 2 digits. Doubling these gives the final answer. Eg if the 2 digits are 17, double gives 34, the final answer is 3417
Example consecutive numbers 10,11,12 multiple of 3 is 18
10+11+12+18 = 51, 51 x 67 = 3417 (child tells you last 2 digits)
To find final number
Double 17 gives 34 So final number is 3417
To find consecutive numbers
Divide 18 by 3 = 6 Subtract 6 from 17 = 11 which is middle number. (10,11,12)