What is the coefficient of the 4th term in the expansion of (1 − x)⁶?

Correct answer: b − 20

(6 3)(−1)³ = −20, so this is the value.

Why the other options are wrong

• a − 35: −35 is a signed (7 3), not (6 3). The right answer is − 20.
• c 42: This does not come from (6 3) = 20, and the sign is negative. The right answer is − 20.
• d 48: This value does not come out of the correct working: (6 3)(−1)³ = −20, so the answer is − 20.