Select the missing numbers from the given responses.

1, 3, 6, 10, 15, ? , 28, 36

প্রদত্ত বিকল্পগুলি থেকে অনুপস্থিত সংখ্যাটি নির্বাচন করুন।

1, 3, 6, 10, 15, ?, 28, 36

Observe the pattern in the sequence:

1, 3, 6, 10, 15, ?, 28, 36

Let us find the difference between consecutive numbers:

3 − 1 = 2
6 − 3 = 3
10 − 6 = 4
15 − 10 = 5

The differences increase by 1 each time.

So the next differences should be:

+6, +7, +8

Now calculate the missing term:

15 + 6 = 21

Check the remaining terms:

21 + 7 = 28
28 + 8 = 36

The pattern fits perfectly.

Therefore, the missing number is 21.

Correct Answer: (D) 21