Chapter: Arithmetic Progression· Mathematics Part 1 (Algebra)
Answer: \(a = 3\), \(d = 4\), \(t_{20} = 79\)
\(t_4 = a + 3d = 15\) …(I)
\(t_9 = a + 8d = 35\) …(II)
(II) − (I): \(5d = 20 \Rightarrow d = 4\). From (I): \(a = 15 - 12 = 3\).
\(t_{20} = a + 19d = 3 + 76 = 79\).