Chocolate maths
Pick the number of times a week that you eat chocolate. This number must be more than one but less than ten.
Multiply this number by 2. Add 5 (for Sunday). Multiply by 50... Can you explain why it works?
Age
11 to 14
Challenge level
Problem
This is cool chocolate maths!!!
Image
- First of all, pick the number of times a week that you eat chocolate. This number must be more than one but less than ten.
- Multiply this number by 2 (just to be bold).
- Add 5 (for Sunday).
- Multiply it by 50.
- Add 1750.
- Add the last two digits from the year you last had a birthday. So if your last birthday was in 2009, add 9, if the your last birthday was in 2011 then add 11.
- Now subtract the four digit year that you were born (if you remember).
You should now have a three digit number. The first digit will be your original number (i.e. how many times you eat chocolate each week). The next two digits give your age. Can you explain why it works?
Student Solutions
Thank you to Gareth Matthews, Llantwit Major Comprehensive School for this solution. Jenny Cook, age 15, The Mount School York, Andrei Lazanu, age 12, School 205, Bucharest, Romania and Clement Goh, age 13, from River Valley High School, Singapore all sent good solutions.
I used algebra to get my answer.
| The problem | The solution | My calculation |
|---|---|---|
| First of all, pick the number of times a week that you eat chocolate. | A | 7 |
| Multiply this number by 2 (just to be bold). | 2A | 14 |
| Add 5 (for Sunday). | 2A+5 | 19 |
| Multiply it by 50. | 100A+250 This multiplies the original number by 100 and adds 250 |
950 |
| Add 1750, then the last two digits of the year you last had a birthday. | 100A+2000+ab |
2709 |
| Now subtract the four digit year that you were born (if you remember). | 100A +2000+ab-cdef Subtracting the year i was born (cdef) from the year I last had a birthday (20ab) gives my age. 100A puts the number A in the hundreds place. |
714 |