523 * 489 using mental math
523 * 500 = 52300 + 52300 + 52300 + 52300 =
11 less groups... sounds complicated. Any other ideas?
Thanks,
Terminator
500 is half of one thousand so 500 times 523 is 1/2 of 523000. Can you do 523000/2 in you head?
489 is 11 less than 500 so after you have 500 times 523, you still need to subtract 11 times 523. What is 10 times 523? Can you subtract that from the 523000/2 you already have? The subtract it once more.
Hello, terminator!
$\displaystyle 523 \times 489\;\text{ using mental math}$
I might be able to do this mentally ... under threat of death.
$\displaystyle (523)(489) \;=\;(500+23)(500-11)$
. . . . . . . . . . .$\displaystyle =\;500^2 - (11)(500) + (23)(500) - (23)(11)$
. . . . . . . . . . .$\displaystyle =\;500^2 + (12)(500) - (23)(11)$
. . . . . . . . . . .$\displaystyle =\;250,\!000 + 6,\!000 -253$
. . . . . . . . . . .$\displaystyle =\;256,\!000 - 253$
. . . . . . . . . . .$\displaystyle =\;255,\!747$
firstly;
you can do this
532
x 489
----
4788
4256
2128
----------
260148
-----------
9x2=18
9x3=27
9x5=45
8x2=16
8x3=24
8x5=40
4x2=8
4x3=12
4x5=20
answer is = 260148
i believe this method is very easy and you just have to pick one number from the bottom and multiply it by all the numbers above
the do the same for the next bottoms number and after all that, you add all of the answer
let me know if you do not understand!!