Tendencias, relaciones entre variables y predicción de valores.
Claves
Interpolar: el valor queda entre los dos puntos vecinos.
Estrategia paso a paso
Señala con el dedo los valores en orden y di en voz baja «sube, sube, baja».
Trampas habituales
Elegir «increased only» cuando al final baja.
Ejemplo resuelto
20 °C → 14,6 mL; 30 °C → 21,3 mL; a 25 °C → entre ambos.
Preguntas de ejemplo
Intenta responder antes de abrir la solución. Las preguntas están en el idioma del examen.
Pregunta 1
Dificultad fácil≈ 1 min
Passage II — River insects and dissolved oxygen (data representation)
Scientists studied a river downstream of an outlet where treated wastewater enters the river. At 5 sites (Sites 1–5), they measured the water temperature and the concentration of dissolved oxygen (DO) at noon. At each site, they also collected insect larvae from 1 $\text{m}2$ of streambed using the same type of net, and they counted the larvae of 2 kinds of insects: mayflies and midges.
Table 1 gives the location and water temperature of each site. Figure 1 shows the DO concentration at each site, and Figure 2 shows the numbers of larvae.
Table 1
Site
Location relative to outlet
Water temperature (°C)
1
2 km upstream
14
2
0.5 km downstream
17
3
2 km downstream
16
4
5 km downstream
15
5
10 km downstream
14
Based on Table 1 and Figure 1, for Sites 2 through 5, as the distance downstream from the outlet increased, the DO concentration:
AA. decreased only.
BB. decreased and then increased.
CC. remained the same.
DD. increased only.
Ver respuesta y explicación
Respuesta correcta: D. increased only.
Explicación
Table 1 shows that Sites 2, 3, 4, and 5 are 0.5, 2, 5, and 10 km downstream. In Figure 1 their DO values are about 5.0, 6.5, 8.0, and 9.0 mg/L, which increase at every step.
The values never decrease, so “decreased only” and “decreased and then increased” are wrong, and they change at every site, so “remained the same” is wrong.
Pregunta 2
Dificultad media≈ 1 min
Passage VII — Solubility of 3 salts (research summary)
The solubility of a substance is the greatest mass of it that can dissolve in a given amount of water at a given temperature. A solution that holds that greatest mass is saturated.
Students measured the solubility of 3 salts (Salts X, Y, and Z) in 100 g of water at 5 temperatures. At each temperature, they added a salt to the water in small portions, stirring for 5 minutes after each addition, until some of the salt remained undissolved. They then filtered the mixture, dried and weighed the undissolved salt, and subtracted that mass from the total mass of salt added. The results are shown in Figure 1.
Based on Figure 1, Salts X and Y had the same solubility at a temperature closest to:
AA. 10°C
BB. 25°C
CC. 40°C
DD. 60°C
Ver respuesta y explicación
Respuesta correcta: B. 25°C
Explicación
Salt Y stays near 36 g. Salt X is 30 g at 20°C and 60 g at 40°C, so it passes 36 g a little above 20°C, at about 24°C. The closest choice is 25°C.
Near 10°C it is Salts X and Z whose lines cross. At 40°C and 60°C, Salt X is far above Salt Y.
Pregunta 3
Dificultad difícil≈ 1 min
Passage V — City noise and bird song (data representation)
Male songbirds sing to defend their territories and to attract mates. Traffic noise is mostly low-pitched, so it easily masks (drowns out) the low-pitched parts of a song.
Researchers studied a songbird species that lives in forests, suburbs, and city centers. For each of 12 males, they measured the background noise level in the male’s territory, in decibels (dB), and the lowest frequency in the male’s song, in kilohertz (kHz). A higher frequency is a higher pitch. Figure 1 shows the results, with a line of best fit. Figure 2 shows the average background noise in each of the 3 habitats at dawn and at noon.
Based on Figures 1 and 2, a male singing at noon in the Downtown habitat would be expected to have a lowest song frequency closest to:
AA. 2.7 kHz
BB. 3.1 kHz
CC. 3.4 kHz
DD. 3.7 kHz
Ver respuesta y explicación
Respuesta correcta: C. 3.4 kHz
Explicación
Figure 2: Downtown at noon averages about 68 dB. Figure 1: the line of best fit at 68 dB is at about 3.4 kHz.
3.1 kHz is the value for Downtown at DAWN (about 58 dB). 2.7 kHz matches the forest (about 40–42 dB). 3.7 kHz is above the line anywhere on the graph.