Forum Replies Created
-
Posts
-
Just to add onto my last comment, I’m finding several examples of where the DS method is just wrong.
Taking the same equation 15 x 16 = 240.
When applying the DS method on the left-hand side you get a 6 x 7 = 42 = 6 (when taking the digit sum)
Here are a number of different examples of where there is an incorrect answer but the DS method says it is correct (i.e. digit sum of right-hand side = 6)
- 15 x 16 = 339
- 15 x 16 = 42342
- 15 x 16 = 4542
- 15 x 16 = 402
- 15 x 16 = 204
- 15 x 16 = 222
- 15 x 16 = 15
- 15 x 16 = 132
- 15 x 16 = 123
- 15 x 16 = 321
- 15 x 16 = 33
- 15 x 16 = 42
- 15 x 16 = 96
This doesn’t look like 90% accuracy to me. Please let me know your thoughts.
I’ve just read 2 chapters of this book, where I have looked at the DS & DD Method of Checking which is intriguing.
However, they don’t seem to be very accurate.
I have found another example that contradicts what was mentioned in chapter 2.
If you do 16 x 15 = 2.40 (which is incorrect because the right answer should be 240).
Both the DD and DS method say the answer is correct. In Chapter 2, it says that the DD method should catch out scenarios where the decimal place is in the wrong place. Am I missing something here?
I would like to know where does the DD/DS method originate from? Do they have mathematical proofs to show the error rate in their usage?