The rules that solve most questions
- Main idea: what the whole passage builds toward, usually stated or implied in the last sentences.
- Detail questions: find the exact sentence that answers the question before looking at the choices.
- Function questions: ask why the author included the sentence (to give background, contrast, an example).
- Eliminate choices that are too broad, too narrow, or contradict the passage.
Traps the wrong answers are built on
- A choice that is true in general but not stated in the passage.
- A choice that repeats words from the passage but changes their meaning.
Worked example
For centuries, sailors relied on the stars to find their latitude, but longitude was much harder to determine at sea. Finding it required knowing the exact time at a reference location while at sea, and the pendulum clocks of the period did not keep accurate time on a rolling ship. In the eighteenth century, the English clockmaker John Harrison built a series of marine chronometers that kept time accurately enough to solve the problem.
Which choice best states the main idea of the text?
- A. Harrison's marine chronometers solved the problem of finding longitude at sea by keeping accurate time on board.
- B. Sailors could not find their latitude until the eighteenth century.
- C. Pendulum clocks were the most accurate timekeepers available to sailors.
- D. John Harrison was the first person to use the stars for navigation.
Answer: A. The text sets up the longitude problem and explains how Harrison's clocks solved it.
Practice set
Answer each question to see whether you're right and why.
0 of 4 answered · 0 correct
- Question 1Medium
For centuries, sailors relied on the stars to find their latitude, but longitude was much harder to determine at sea. Finding it required knowing the exact time at a reference location while at sea, and the pendulum clocks of the period did not keep accurate time on a rolling ship. In the eighteenth century, the English clockmaker John Harrison built a series of marine chronometers that kept time accurately enough to solve the problem.
Which choice best states the main idea of the text?
Show answer and explanation
Answer: A
The text sets up the longitude problem and explains how Harrison's clocks solved it.
- B: The text says latitude was found from the stars long before.
- C: The text says pendulum clocks failed at sea.
- D: The text says sailors had used the stars for centuries.
- Question 2Medium
Coral reefs cover a tiny fraction of the ocean floor, yet they support roughly a quarter of all known marine species. Reef-building corals depend on algae that live inside their tissues and supply them with food. When water becomes too warm, corals expel these algae and turn white, a process called bleaching. If high temperatures last too long, the corals can die.
Based on the text, why are high water temperatures a threat to corals?
Show answer and explanation
Answer: D
The text says heat makes corals expel the algae that feed them, and prolonged heat can kill them.
- A: The text says prolonged bleaching can kill corals.
- B: The text doesn't say heat increases species.
- C: Nothing links temperature to reef area.
- Question 3Medium
The printing press developed by Johannes Gutenberg around 1440 used movable metal type, which could be rearranged to print any page. Before it, books in Europe were mostly copied by hand, a slow and costly process. Printed books could be produced far faster and more cheaply, and within decades presses had spread to cities across Europe.
Which choice best describes the function of the second sentence in the text?
Show answer and explanation
Answer: C
The second sentence describes hand-copying, setting up the contrast with faster printing.
- A: The date is in the first sentence.
- B: The text doesn't name any cities.
- D: Movable type is explained in the first sentence.
- Question 4Medium
Penicillin was discovered in 1928 when Alexander Fleming noticed that a mold growing on one of his bacterial cultures had killed the bacteria around it. Fleming published his observation, but it was more than a decade before other scientists developed a way to purify and produce the drug in large amounts. By the mid-1940s, penicillin was saving many lives by treating bacterial infections.
According to the text, what happened after Fleming published his observation?
Show answer and explanation
Answer: B
The text says it took over a decade before others developed purification and production.
- A: The text doesn't say Fleming treated patients.
- C: The text says penicillin treated bacterial infections.
- D: The text says the mold killed bacteria.
Questions people ask
Is this central ideas and details practice like the real SAT?
The questions follow the format of the digital SAT's Information and Ideas domain: a short text with one blank or question and four choices. They are written for this site; they are not official College Board questions.
Where is the domain on the test?
Information and Ideas is one of the four content domains of the SAT Reading and Writing section, alongside Craft and Structure, Expression of Ideas, Standard English Conventions.