Can you also solve this problem with solution?

Question

Twelve days before Ramadhan, Usman planned to give his mother a gift. On the first day, he sent one gift, on the second day he sent two gifts, on the third day, three gifts and so on. How many gifts did usman send his mother aftee twelfth day?

Answer 1

Because there is a constant difference of 1 between the numbers in the series: 1, 2, 3, ...., 12, it is an arithmetic series, where the first number is 1, the last number is 12 and there are 12 numbers in the series

the sum of a arithmetic sequence is n (a1 + an)/2.

where n is the number of elements in the series and a1 and an are the first and last elements in the series.

Here n = 12, a1 = 1 and an = 12

so sum is 12 (1 + 12)/2 = 78