HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 33

Fractions on the hp 39gs and hp 40gs 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 reason for this is that the Fraction setting can be a little deceptive. Begin by selecting Fraction in the MODES view, leaving the accompanying number as the default value of 4. Most calculators have a fraction key, often labeled , that allows you to input, for example, 12 3 as 1¬2¬3 or something similar. What these calculators usually won't do is allow you to mix fractions and decimals. A calculation such as 12 3 + 3⋅ 7 will usually give a decimal result: most calculators 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. When making the hp 39gs and hp 40gs HP 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 12 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 ½ 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 else "order of operations" problems may occur, such as 123 * 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. Some examples are... (using a setting of Fraction 4 or higher) 1 + 4 = 17 3 5 15 3 1 − 4 1 = −11 32 6 33