40
F
F
r
r
a
a
c
c
t
t
i
i
o
o
n
n
s
s
o
o
n
n
t
t
h
h
e
e
h
h
p
p
3
3
9
9
g
g
+
+
Earlier we examined the use of the
MODES
view, and the meaning of
Number
Format
. We discussed the use of the settings
Fixed
,
Scientific
and
Engineering
, but left the setting of
Fraction
for later. The
Fraction
setting can be a little deceptive.
Most calculators have a fraction key, often labeled
b
a
c
, that allows you to
input, for example,
2
1
3
as
1 2 3
¬ ¬
or something similar. What these
calculators usually won’t do is allow you to mix fractions and decimals.
On most calculators
2
1
3 7
3
+ ⋅
will give a decimal result - the calculator will
not attempt to convert the
3 7
⋅
into a fraction. The reason for this is that
while some decimals like 0.25 are easy to convert to a fraction, others, such
as recurring ones, are not so easy. Most calculators opt for the easy option
of switching to a decimal answer in any mixture of fractions and decimals.
The makers of the hp 39g+ took a very different approach. Once you select
Fraction
mode, all numbers become fractions - including any decimals.
The first point to remember is that there is no
provision for inputting mixed fractions such as
2
1
3
. Fractions are entered using the divide
key and, while the calculator is quite happy
with improper fractions such as
5/3
, it
correctly interprets
1/2/3
as one half divided by 3 and gives a result of
1/6
. The solution to this is simply to enter mixed fractions as
(1+2/3)
.
Calculator Tip
You need to be careful with brackets or “order of
operations” problems may occur, such as
2
1
3
*
1
5
being
interpreted as
1+(2/3*1/5)
rather than as it should be:
(1+2/3)*1/5
. When in doubt, use brackets for mixed
fractions.
