4.8.5 Human Calculator

Now, let’s look at a quick way to attack division by nine.

Activity symbol Activity: The Human Calculator

Videoclip symbolWatch this short video to discover the power of your brain:

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Now see how quickly you can perform these calculations in your head.

(a) 2154 division nine

Hint

Hint symbol

Comment

Write down the first number of the dividend, then use addition. Watch out for carries!

Solution symbol

Answer

(a) multiline equation line 1 two one five four prefix division of nine line 2 two three eight super one 12 cubed line 3 two three nine cap r times three

Thus, 2154 division nine equals 239 cap r times three.

(b) three one zero two one two prefix division of nine

Solution symbol

Answer

(b) multiline equation line 1 three one zero two one two prefix division of nine line 2 three four four six seven super one nine super zero line 3 three four four six eight

Thus, three one zero two one two prefix division of nine equals 34 comma 468.

(c)three two six four four one two division nine  (This one is tough—you might need to write the shortcut out!)

Solution symbol

Answer

multiline equation line 1 three two six four four one two prefix division of nine line 2 three five super one one super one five super one nine squared zero times super two 22 super four line 3 three six two six super one one two cap r times four line 4 three six two seven one two cap r times four

Thus, three two six four four one equation left hand side two division nine equals right hand side 362 comma 712 cap r times four.

Aren’t you impressed by the power of your brain? You should be! Of course, the real math is understanding why this trick works, but you’ll have to study much more math to find that out.

Cartoon of a brain showing through someones head
Long description

Now you have finished the optional activities as well it is time to move onto Unit 5 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]   and continue to work with numbers. To be precise, you will work with various units of measurement and negative numbers. See you there and keep going!

4.8.4 Here’s the Trick!