Funny way to divide by seven (Posted on 2018-01-12)
"This special big number of mine allows me to get a correct answer of dividing it by 7 by simply erasing its second digit..." - declared Danny.
After a minute or two his father, W.G.
quipped: "I know what digit was erased!"
clearly, there are no 2 digit numbers that qualify.
Assuming 3-digit number 100a+10b+c,
100a+10b+c=7*(10a+c), try b=0 (later b=1,2 etc)
30a+10=6c
a=1 c=5
7*15=105, so the erased digit was 0, as assumed .
OBVIOUSLY any number of zeroes can be added following 105.
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