From the BEATCALC
mailing list:
a weekly service from B. Lee Clay,
archived here by the Math Forum.
To subscribe to the BEATCALC mailing list,
write to BEATCALC@aol.com.
Dividing a 2- or 3-digit number by 35
Select a 2-digit number. (Choose larger numbers when you feel sure about the
method.)
Multiply by 2.
Divide the resulting number by 7.
Move the decimal point 1 place to the left.
Example:
If the number chosen to divide by 35 is 61:
Multiply by 2: 2 x 61 = 122.
Divide by 7: 122/7 = 17 3/7
Move the decimal point 1 place to the left: 1.7 3/7
So 61 divided by 35 = 1.7 3/7.
See the pattern?
If the number chosen to divide by 35 is 44:
Multiply by 2: 2 x 44 = 88
Divide by 7: 88/7 = 12 4/7
Move the decimal point 1 place to the left: 1.2 4/7
So 44 divided by 35 = 1.2 4/7.
Division done by calculator will give repeating decimals
(unless the original number is a multiple of 7), truncated
by the limits of the display. The exact answer must be
expressed as a mixed number.