© 2000 T
EXAS
I
NSTRUMENTS
I
NCORPORATED
TI-15: A
Guide
for
Teachers
13
Comparing Costs
(Continued)
•
What happens if you multiply each solution by
6 to check it?
For the remainder form, you have to multiply
586 x 6 and then add 4 to get the total cost of
$3520. You can multiply 586
2
/
3
x 6 in fraction
form to get $3520. If you enter
586.666667 x 6
and
press
®
, you get
3520
, but that doesn’t make
sense because 6 x 7 doesn’t end in a 0!
If you enter
586.66667
, then fix the decimal
quotient to hundredths since it is money, and
then find 586.67 x 6, you
still
get 3520.00, which
still doesn’t make sense because 6 x 7 = 42. If you
clear the calculator and enter
586.67 x 6
, and
press
®
, then the display reads
3520.02
, which
does make sense.
•
As a school, which form of the quotient would
you want to use?
Responses may vary. Some students may want to
use the decimal form, since it is the closest to the
representation of money. Some students may
want to use the integer quotient and remainder
form and suggest that the Central Office pay the
$4.00 remainder.
Although the fraction form of the quotient
describes the exact quantity that each school
should pay, most students will recognize, by
comparing it to the decimal form, that the
fraction form is not easily translated into money.
When you fix
586.666667 to 2
decimal places, and
then multiply by 6, the
calculator “remembers”
the original number and
uses it as the factor.
The product rounded to
the nearest hundredth,
using the original factor,
is 3520.00. When you
enter 586.67, the
calculator uses this
number for the factor,
showing the actual
product of 3520.02.
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