Start from row 1's number 1.

From no. 1 to no. 3 in row 2, add 2.
3 = 1 + 2

From no. 3 to no. 6 in row 3, add 3.
6 = 1 + 2 + 3

From no. 6 to no.10 in row 4, add 4.
10 = 1 + 2 + 3 + 4

From no.10 to no.15 in row 5, add 5.
15 = 1 + 2 + 3 + 4 + 5


Notice that the last number in the sum for a particular row's greatest number is always the same as the row number.

The sum always has a different last number for every row, which is 1 bigger than the preceding row's last number.


So for row 200, the last number in the sum would be 200 for the greatest number

Greatest number

= 1 + 2 + 3 + 4 + 5 + 6 + .... + 197 + 198 + 199 + 200



Now notice that

1 + 200 = 201
2 + 199 = 201
3 + 198 = 201
4 + 197 = 201

We can pair the numbers up such thay they always add to 201 for each pair.

Eventually we get to

...
...
98 + 103 = 201
99 + 102 = 201
100 + 101 = 201


We have finished pairing the numbers.

There are 100 pairs of 201


So greatest number = 100 x 201 = 20100

This also tells you that there are 20100 numbers from Row 1 to Row 200

Is there any other ways instead of using this method ? Because I don't quite understand

Just edited. Read through again and if it's still not clear I'll think of something else.

Ok, thx for the helping