Download Tricks help solve math mistakes

Farm Management
Wallaces Farmer
www.FarmProgress.com ● February 2015
55
Tricks help solve math mistakes
O
LD-TIMERS used some simple
mathematical relationships to
help balance their accounts that
we technology-dependent youngsters may
have forgotten. We’ll illustrate a couple.
Key Points
On the
Money
By JOHN OTTE
Find transpositions
You’re attempting to balance your checkbook. You’ve clicked off all the entries in
your register against the bank statement.
The balance in your register fails to match
■ If the discrepancy divided by 9 gives a
round number, look for a transposition.
■ Dividing difference by 2 and looking for
that number can detect changed signs.
■ Keeping a rough tab on auction
spending can keep you within budget.
the balance on the bank statement.
Calculate the difference between your
bank statement and your check register.
Divide that difference by 9. If that calculation generates an exact number, that is no
digits beyond the decimal point, go back
to your check register and look for a transposition in your register.
For example, your bank statement
shows checks of 452 + 687 + 387 + 415,
which total 1,941. Your register shows a
total of 2,121. The difference is 180, which
divided by 9 gives an even 20. Looking
through your register, you find you converted the 687 to 867.
You changed signs
Suppose the difference is not evenly divisible by 9. Divide the difference by 2.
Go through your register. If you find that
number, check the sign. Again suppose
your bank statement totals those four
numbers to 1,941. Your tally shows 567.
The difference is 1,374, which divided by 2,
gives 687. You fat-fingered your calculator
keyboard and subtracted the 687 rather
than adding it.
Suppose you’ve advanced beyond the
antiquated calculator and you’re using
Excel. You can still fat-finger the keyboard
and end up with a discrepancy.
Of course, neither one of those tricks
will help you if you’ve made more than
one error.
Alternate to carrying
An acquaintance is good at running numbers in his head. How?
Suppose you’re in the hardware store
to buy an airless paint sprayer, $727, plus
5 gallons of paint, $385.
Traditionally, you’d figure 7 plus 5 is 12,
write down the 2, carry the 1; then 2 plus 8
is 10, plus the 1 you carried is 11, carry the
1; and then 7 plus 3 is 10 again, plus the 1
you carried, is $1,112.
My acquaintance says $385 is $15 short
of $400. Then $400 plus $727 is $1,127. Next
minus 15 leaves $1,112.
Suppose you’re at an auction. Keeping
a ballpark tab on how much you’ve already
spent might keep you from overrunning
your line of credit at the bank.
Otte is farm management editor for Farm
Futures magazine. See FarmFutures.com.
Quick addition
Bill Jesina
Grain, Pork & Beef Producer
Toledo, IA
fcsamerica.com/billjesina
S
UPPOSE your wise-guy grandson
thinks he’s pretty smart. Have him
write down a five-digit number. You
write one just below his. Have him
write another. You write another one
just below his. You write a fifth fivedigit number, and without batting an
eyelash, you tally the total, plus you
start from left to right, rather than the
traditional right to left.
How do you do it? After he writes
his first number, you write a number
such that his number and your
number total 99,999. Do that again.
You write down the final five-digit
number. The total will be your five
digits, plus a 2 in front, less 2 on the
end.
See how long the smart aleck
needs to figure it out.