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# Help

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MathWhiz likes to play a fun number trick on her friends. She tells them to think of a number. She then tells them to subtract their number from 1 and multiply the result by 4. To this product she tells them to add half the difference when 6 is subtracted from 10 times their original number.

(a) If I use the number 3 and follow MathWhiz's steps, what number will I get?

(b) If you correctly apply MathWhiz's steps to any number, and then tell MathWhiz your result, how can MathWhiz quickly figure out what number you started with?

Mar 14, 2020
edited by Guest  Mar 14, 2020

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Let  X  be the original number.

Subtract that number from 1   --->   1 - X

Multiply this result by 4:          --->   4(1 - X)

Add half the difference when 6 is subtracted from 10 times the original number:

--->   4(1 - X) + ½(10X - 6)

Final result:                            --->   4 - 4X + 5X - 3   =   X + 1

a)  Let  X = 3:  --->   X + 1  =  4

b)  To find the original number from the answer:  Subtract 1.

Mar 14, 2020