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<blockquote data-quote="InsaneCdn" data-source="post: 479669" data-attributes="member: 11791"><p>Basic math multiplication facts strategies...</p><p>Here's hoping I can remember them all!</p><p></p><p>x 2 = double it.</p><p>x 3 = triple it.</p><p></p><p>(most of us can do those in our heads, so far so good).</p><p></p><p>x 4 = double, then double again (NNN x 4 = NNN x 2 x 2)</p><p>x 5 = add a zero to then end, then take half of that (7 x 5 = 70 / 2 = 35)</p><p>x 6 = double, then triple (in that order)</p><p>x 7... you don't do. Memorize 7x7. Everything else fits under another rule!</p><p>x 8 = double, then double, then double again</p><p>x 9 = OK, not <u>quite</u> so easy to explain, but easy to do; only works for up to 9x9, though. 9 x NNN = (NNN-1) concatenated with (9 - (NNN-1)): 9x4 = 3 || 6 = 36, 9x8 = 7 || 2 = 72. (|| = concatenate)</p><p>x 10 = don't tell me ANYBODY memorizes that one!... just add a zero to the end.</p><p></p><p>alternate x 9 rule... triple, then triple again, but for most of us, tripling is too slow. It does work, though.</p><p></p><p>Basic skills are:</p><p>- double</p><p>- triple - the only one that takes any kind of effort.</p><p>- add zero to end</p><p>- half - opposite of double</p><p>- one mental trick (9s)</p><p>- one memorization (7x7)</p><p></p><p>For higher number multiplication, any number with multiple divisors, is easy to break down... 11s is a trick, 12s you break down (NNNx2x2x3), 13 is "do the work", so is 14, 15 = ...x10x5, and so on. Now, they usually do these as multi-column multiplication, but we used to go to 20 at least using "rules"</p></blockquote><p></p>
[QUOTE="InsaneCdn, post: 479669, member: 11791"] Basic math multiplication facts strategies... Here's hoping I can remember them all! x 2 = double it. x 3 = triple it. (most of us can do those in our heads, so far so good). x 4 = double, then double again (NNN x 4 = NNN x 2 x 2) x 5 = add a zero to then end, then take half of that (7 x 5 = 70 / 2 = 35) x 6 = double, then triple (in that order) x 7... you don't do. Memorize 7x7. Everything else fits under another rule! x 8 = double, then double, then double again x 9 = OK, not [U]quite[/U] so easy to explain, but easy to do; only works for up to 9x9, though. 9 x NNN = (NNN-1) concatenated with (9 - (NNN-1)): 9x4 = 3 || 6 = 36, 9x8 = 7 || 2 = 72. (|| = concatenate) x 10 = don't tell me ANYBODY memorizes that one!... just add a zero to the end. alternate x 9 rule... triple, then triple again, but for most of us, tripling is too slow. It does work, though. Basic skills are: - double - triple - the only one that takes any kind of effort. - add zero to end - half - opposite of double - one mental trick (9s) - one memorization (7x7) For higher number multiplication, any number with multiple divisors, is easy to break down... 11s is a trick, 12s you break down (NNNx2x2x3), 13 is "do the work", so is 14, 15 = ...x10x5, and so on. Now, they usually do these as multi-column multiplication, but we used to go to 20 at least using "rules" [/QUOTE]
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