## Forum Replies Created

Viewing 7 posts - 1 through 7 (of 7 total)
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• in reply to: digit sum #10754
Participant
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6874 has the same digit sum as 6775 because 6874 = 6874 – 99. In fact, they have the same digit difference because the difference is a multiple of 11.

in reply to: DD Method #10753
Participant
• Topics: 4
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And if you have a decimal point, it’s

E O E O . E O E O

in reply to: 3 Digit Squaring #8509
Participant
• Topics: 4
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I came here to ask this exact question, so I’m glad I looked at previous replies first.

Is there an easier way of doing this? The more digits I want to square, the harder this task will get. For example, if I want to square 12345, then I don’t want to be doing 1234 * 1235 at first. What do you think?

in reply to: DD: The number 10 #8506
Participant
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This makes sense because 10 * 10 = 100, and the DD of 100 = 1 = -1 * -1.

Still, sometimes I have to add 11 to the final answer, such as when I multiply 21 by 58. The DD method would show -3, which is the same as 8, which is the same as the DD method for the answer, 1218.

in reply to: DD Method vs DS Method #8505
Participant
• Topics: 4
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Actually, I came up with one. I multiplied 35 * 67 and got 2455 instead of 2345, and I knew it was wrong only because of the DS method.

So the DS method will fail where the DD method succeeds when the correct answer is added to a non-zero multiple of 11 that is not a also a multiple of 9. So coming up with 3335 would have made the DS and DD methods both succeed, but the answer would have been wrong.

in reply to: DD Method vs DS Method #8367
Participant
• Topics: 4
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But I do have a question myself. Where would the DS method catch something that the DD method wouldn’t? The lecture videos didn’t say in that section.

in reply to: DD Method vs DS Method #8365