HP Calculators by HP - Manual (Page 7)

Figure 1: Mixed Fraction format Figure 2: 30.5 becomes 30 1/2
Figure 3: The first two terms, using ANS Figure 4: 38 3/8” in 2077
Answer Key for Two Trends
In this short activity, students match the increasing trend of San Antonio precipitation to the decreasing
trend of Seattle precipitation to estimate the year in which both cities have the same amount of rainfall.
1. Repeat the same process on the HP 39gs, but with an initial starting value of 38 2/5 (see Figure 5)
and a decrease of 2/3 (Figure 6). The values are shown in the table below.
Figure 5: Starting the Seattle sequence Figure 6: Using ANS again
Year San Antonio Seattle
2007 30 1/2 38 2/5
2017 31 5/8 37 11/15
2027 32 3/4 37 1/15
2037 33 7/8 36 2/5
2047 35 35 11/15
2057 36 1/8 35 1/15
Looking at the table, it is clear that the two cities would be predicted to have identical rainfall totals in one
of the years between 2047 and 2057. This is definitely within the life expectancies of the students!
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