Question 183·200 Super-Hard SAT Reading Questions·Information and Ideas

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Duckweed Growth under Three Light Treatments

Light treatment	Initial combined frond count	Final combined frond count
Continuous red	100	260
Alternating red and blue	100	220
Continuous blue	100	180

Researchers grew two duckweed species, Lemna minor and Spirodela polyrhiza, together under three light treatments. Each culture initially contained 50 fronds of each species, and both species increased under every treatment. Species-specific imaging showed that L. minor accounted for between 70% and 75% of the combined increase under alternating red and blue light, no more than 50% of the combined increase under continuous red light, and exactly 50% of the combined increase under continuous blue light.

Taken together, the text and table best support which statement about the cultures at the end of the experiment?

When a command-of-evidence question combines a table with percentages or ranges, convert the table values into net changes first. Then use the lowest and highest permitted percentages to establish bounds. A comparison is certain only when the entire possible range for one quantity lies above or below the range for the other quantity.

Hints

Hint 1
Calculate net growth
For each treatment, subtract the initial combined frond count from the final combined frond count.
Hint 2
Use percentage bounds
For alternating light, apply the lowest stated percentage to the combined increase. For continuous red light, apply the highest permitted percentage.
Hint 3
Restore the initial count
After calculating each species-specific increase, remember that every culture began with 50 L. minor fronds.

Step-by-step

Step 1
Find each treatment's combined increase
Subtract the initial combined count of 100 from each final count. The increases were 160 under continuous red light, 120 under alternating light, and 80 under continuous blue light.
Step 2
Determine the relevant species counts
Under alternating light, L. minor produced between 70% and 75% of the 120-frond increase. Its increase was therefore between $0.70(120)=84$ and $0.75(120)=90$ , giving it a final count between 134 and 140.
Step 3
Compare the numerical bounds
Under continuous red light, L. minor produced no more than 50% of the 160-frond increase. Its increase was at most $0.50(160)=80$ , so its final count was at most 130. Even the lowest possible alternating-light count, 134, exceeds this maximum.

Question 183·200 Super-Hard SAT Reading Questions·Information and Ideas

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