41
Some examples are… (using Fraction 4 or higher)
1.
1417
3515
+=
2.
11 1
34 1
32 6
=−
The second point to remember involves the method the hp 39g+ uses when
converting decimals to fractions, which is basically to generate (internally and
unseen by you) a series of continued fractions which are approximations to
the decimal entered. The final fractional approximation chosen for display is
the first one found which is ‘sufficiently close’ to the decimal.
The trap lies in what constitutes ‘sufficiently close’, and this is determined by
the ‘4’ in Fraction 4. Roughly, the calculator will use the first fraction it
finds in its process of approximation which matches the decimal to that
number of significant digits.
For example, a setting in the MODES view of…
Fraction 1 changes 0.234 to
3
13
which is actually 0.2307692…
(matching to at least 1 sig. fig.)
Fraction 2 changes 0.234 to
7
30
which is actually 0.2333333…
(matching to at least 2 sig. fig.)
Fraction 3 changes 0.234 to
11
47
which is actually 0.2340425…
(matching to at least 3 sig. fig.)
Fraction 4 changes 0.234 to
117 234
500 1000
or
which is exactly 0.234
Essentially, the value of ‘n’ in ‘Fraction n’ affects the degree of
precision used in converting the decimal to a fraction. As was said earlier,
the calculator will use the first fraction it finds in its process of approximation
which matches the decimal to that number of significant digits.
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