What will be the 24th term of the AP (−15, −9, −3, ...)?

Correct answer: 123

For an arithmetic progression, use a_n = a + (n − 1)d. The first term is a = −15, and the common difference is d = −9 − (−15) = 6. Substituting n = 24 gives a_24 = −15 + (24 − 1)6 = −15 + 23 × 6 = −15 + 138 = 123. Thus option B is correct. The negative sign belongs to the first term, while the common difference is positive because the sequence increases by 6 each time. A likely mistake is to write −15 + 24 × 6, which counts one extra gap and gives 129, or to mishandle the negative first term. Checking the sequence rule confirms that 23 jumps from the first term lead to the 24th term.