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Hi Aaron,
The round up method simply states that the last digits add up to 10 and the other digits add up to 9. There is no concept of left to right or right to left here. So was not sure what you meant?
Can you give me an example of what kind of scenarios you will need to do mental math for trigonometry or geometry? Those are generally not areas where we need to do mental math in the real world or in exams.
Multiplying large numbers come with practice and using the mind palace. You have to use a combination of rounding up and the methods we have covered to do the mental calculation. It will not be as easy and fast as multiplying lower digit numbers.
You don’t always have to make all numbers add up to 9.
The number of digits the rounded-up value will have will depend on how much you round up to.
If you round up 3898 to 10,000 you would have rounded up by 6102 which has 4 digits.
If you round up 3898 to 4,000 you would have rounded up by 102 which has 3 digits.
If you round up 3898 to 3,900 you would have rounded up by 02 which has 2 digits.So in this scenario, you shouldn’t do the addition of 3 + 4 + 2 = 9.
Let me know if this clarifies.
When you round up 3898 to 4000 you will have to add a 3 digit number to 3898 to get 4000. So you don’t have to add the 3 + 4 + 2 to get 9.
The amount you round up will have one digit lesser than the original numbers.
Both 3898 and 4000 are 4 digit numbers so the amount you have to round up has to be a 3 digit number which is 102.
How many numbers
Hi Aarin,
Thank you for taking the time to write suggestions.
1. I didn’t quite understand the first suggestion. Are you saying we teach to calculate from right to left in Chapter 8?
2. For the second point on including percentages, fractions etc, I will add it to my backlog and will work to incorporate it into the book and course. I have purposely kept some of the more complicated stuff out of the book so that it remains relevant to most people reading the book or watching the course. I will try to create a course companion so that it becomes useful.
3 & 4. For the next two points which are sort of interlinked which is to remember numbers in your head and carrying over numbers, I would encourage you to read this community post – https://ofpad.com/topic/is-only-the-calculation-performed-in-the-mind/
It probably has the exact answer that you are looking for. Let me know if it doesn’t answer the question.5. Remembering to calculate from left to right comes with practice. If you do it enough number of times, it will become the only natural way to do mental math.
6. The only way to be 100% sure is to of course do the math problem again. Both methods rely on estimation and has an accuracy of >90%. Using both methods together will increase the accuracy even further because the chances of both methods not catching it combined is pretty slim. If I find a method that has even more accuracy, I will make sure I include it.
Let me know if this answers all your questions. If you do enjoy the book, please don’t forget to leave a review. It is really helpful to reach more students.
Hey Honorous,
Glad you were able to figure it out.
No question is a bad question.
I will just highlight the steps here in case it will help other students get clarity.
We are dividing 47 / 12
12 x 3 = 36
So 3 is the quotient.
47 – 36 = 11
11 is the reminder.
If you wanted to calculate decimal places you would add 0 to 11 and continue dividing by adding a decimal point. But since we are interested in getting the reminder we won’t do that.
Hope this clarifies. Feel free to ask anything that you need help with.
Hey Faruuq,
Digit sum can only verify your answer with 90% accuracy.
If you want a higher level of accuracy you can use the DS method in conjunction with the DD method. However even that is not 100%.
The only way to be 100% sure your answer is correct, is to do the calculation again.
Hope this clarifies.
Hi Areadien,
If you insist on using the Stem Method, then the best stem number to use is 20.
However, unless you are practising stem multiplication, you should be using the LR method to do the multiplication of 35 x 5.
With the LR method, it is only 3 simple steps:
1) 3 x 5 = 15
2) 5 x 5 = 25
3) Putting it together we get 175.Hi Areadien,
Yes, you are right. Both methods are not 100%. They are meant to check your answer with a reasonable level of accuracy but there will always be cases where they don’t catch the error.
Hi Areadien,
The easiest way is to use the Bridge or the Vitruvian Man method. But yes, the longer the problem the harder it is going to be do it.
Hi Adreadien,
In this case you will retain the -1 as -1 instead of adding 11 to make it positive. Here is how that will turn out:
Addition
Check: 14 + 10 = 24
DD: 3 – 1 = 2Subtraction
Check: 14 – 10 = 4
DD: 3 – -1 = 4
DD: 3 + 1 = 4Multiplication
Check: 14 * 10 = 140
DD: 3 * -1 = (0+1) – 4
DD: -3 = -3Division
Check: 14 / 10 = 1.4
DD: 3 / -1 = 1 – 4
DD: 3 / -1 = -3
DD: 3 = -3 * -1I will add this scenario to the content during the next update.
Let me know if this answer clarifies your question.
Hi Areadien,
As far as I know, there is no scenario where the DD method will fail where the DS method succeeds.
The DD method is more accurate than DS Method. You can be sure 90% of the time with the DS method. However, with the DD method, you will have more than 95% certain.
We still cover the DS method because it is a lot faster to do than the DD method.
Hi Mohammad,
Welcome to the forum. I am guessing the lie is you met Princess Diana. 😉
What habit do you want to focus on first?
Hi Rohit,
Welcome to the community. Looking forward to seeing you start your habit challenge in the community.
Hi Arindam
Happy to provide you with accountability. Please fill the habit challenge workbooks and post it in your habit challenge section of the community.
Looking forward to your updates in the habit challenge Arindam
Hi Arindam,
Please complete all the workbooks in the habit challenge and post it here so that we can follow along your journey and give you accountability.