Short SAT Lessons with Worked Examples
Each caption-first video or illustrated lesson shows one mistake, the correct reasoning and a related practice path. The examples are independent of College Board and free to view without an account.
Algebra: distribute before solving
For 4(x − 2) = 2x + 10, distribute 4 to both terms: 4x − 8 = 2x + 10. Then 2x = 18, so x = 9. Forgetting to multiply −2 by 4 changes the problem.
Words in Context: follow the clue
A rough map becomes more precise after surveys reveal small inlets. Precise means detailed. Temporary is not supported because the passage says nothing about duration.
Percentages: check the new base
$80 rises by 25 percent to $100, then falls by 20 percent of $100 to $80. The second change uses the new base; subtracting 20 from 25 misses that relationship.
Grammar: join complete clauses
The telescope recorded the path, and the team compared the images. Each side is a complete clause. A comma plus and joins them; a comma alone creates a splice.
Rhetorical synthesis: serve the goal
If two programs donate produce and the task asks for a similarity in community contributions, state that both donate. True details about dates or growing methods do not serve that goal.
Semicolon boundary: join two complete clauses
The archive closes at six; the volunteers keep cataloging online. Each side can stand alone as a sentence. A comma by itself would create a comma splice. Read the exact answer choices because a comma plus a coordinating conjunction can also be a valid join.
Subject-verb agreement: find the real subject
The stack of lab reports is on the desk. Stack is singular, and the phrase of lab reports does not change the verb. Remove that phrase to check the core sentence: the stack is on the desk.