Arithmetic Progressions
NCERT Exemplar Ch 05
CBSE_NCERT_EXEMPLAR_CH05
Grade 10
Question:
If the common difference of an AP is $5$, then what is $a_{18} - a_{13}$?
$5$
$20$
$25$
$30$
Step-by-Step Solution
Key Concept: $a_n - a_m = (n - m)d$.
Stepwise Solution:
$a_{18} - a_{13} = (a + 17d) - (a + 12d) = 5d$. [0.5 Mark]
$5(5) = 25$. [0.5 Mark]
Marking Scheme:
• Expressing difference in terms of $d$: 0.5 Mark
• Evaluating $5(5) = 25$: 0.5 Mark
Correct Answer: $25$
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