The marble counts represent the sum of the first 25 natural numbers. Using the sum formula Sn = n(n + 1) / 2 with n = 25, the total calculation is 25 x 26 / 2, which gives 325 marbles.
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With initial salary of 5,00,000 and annual increment of 20,000, his earnings form an AP. Solving 7,00,000 = 5,00,000 + (n – 1) x 20,000 gives n = 11, meaning his income reaches 7,00,000 after 10 years.
The two-digit numbers divisible by 3 range from 12 to 99, forming an AP with common difference 3. There are 30 such numbers and applying the arithmetic sum formula gives a total sum of 1665.
Given a + 2d = 12 and a + 49d = 106, solving these simultaneous equations yields first term a = 8 and common difference d = 2. Therefore, the 29th term evaluates to 8 + 28 x 2 = ...
In this sequence, the first term is 11 and common difference is -3. The explicit nth term simplifies to tn = 14 – 3n, while its recursive rule is stated as t1 = 11, tn = tn-1 – 3 for ...