MAGIC TRICKS "Recurring Number Magic"

Effect
You write down the following 8 digit number on a piece of paper:

1 2 3 4 5 6 7 9

Then ask a friend to circle one of the digits. Say that they circle number 7.

You then ask your friend to multiply the 8 digit number by 63, and magically the result ends up being:

1 2 3 4 5 6 7 9
x 6 3
7 7 7 7 7 7 7 7 7

with the answer as a row of the chosen number 7.

The Secret
When your friend circles a number, you need to multiply the chosen number by 9 in your head - if 3 was chosen you would work out 3 x 9 = 27. Then you need to ask your friend to multiply the 8 digit number by the number you have just worked out. In the case of 3 being chosen you ask your friend to multiply 12345679 by 27 and you magically get the answer 333333333.