Roughly 3 months in advance of the 2018 Mental Calculation World Cup, the competitors have now been informed of this year’s Challenge Task. Every year the competition includes 10 rounds:
- addition, multiplication, square roots and calendar dates
- a difficult “challenge task” announced some time before the competition
- 5 “surprise” rounds unknown to any competitor beforehand
This year the challenge task will be a series of tasks of the following type:
256 x 441 + 56052768 / 628
123 x 789 + 3046308 / 124
388 x 209 + 42498048 / 512
471 x 980 + 12178296 / 216
The tasks should be solved in the given order. No intermediate results are allowed to be written down. And as usual: A correctly solved tasks scores one point. A wrongly solved (or skipped) task scores -1 point.
The two numbers to be multiplied always have 3 digits each, and the result of the division is always a guaranteed to be a five-digit integer number.
Any questions should be directed at Ralf Laue [info@recordholders.org], the organizer of the Mental Calculation World Cup.
Good luck to everyone!
Which would be the best approach to solve the task? How many tasks would a participant of the World Cup do in ten minutes?
The best approach to solve the task is a challenge for the competitors – I will also be competing in the Mental Calculation World Cup and will keep my method secret until after the competition.
I only tried one question so far and it took 2 minutes 30 seconds… with practice I’m sure I can do 10+ questions in ten minutes.
However, this is not my best type of calculation, and I expect that some calculators trained with soroban maybe be able to do 50+ in 10 minutes.
The results will be available here and on the competition website soon after the event, and then we will know!
What struck me immediately is that 256 × 441 = 336². The divisions are very interesting, modulo calculation is very helpful.
For example: 6308 “contains” no more than 2² so the answer of the division will be an odd number, ending on 17 or 67, in this case the answer is 24567.