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Which term of 4, 9, 14, ... equals 89?
A17th
B18th
C19th
D20th
Answer & Solution
Correct answer: B. 18th
1. Here a = 4 and d = 5; let a_n = 89.
2. 89 = 4 + (n - 1) * 5.
3. (n - 1) * 5 = 85, so n - 1 = 17.
4. Hence n = 18.
_Source: Selina Concise Mathematics Class 10, Ch on Arithmetic Progression (Mistral OCR'd PDF), section on nth term_
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