Algebra-2

The missing number is 21.

 

Here's the reasoning: In Pascal's Triangle, each number (except for the 1s on the edges of each row) is the sum of the two numbers directly above it in the previous row.

 

For the eighth row where the missing number is located, we look at the seventh row which has the numbers 1, 6, 15, 20, 15, 6, 1.

 

The number we need to find in the eighth row has the two numbers 15 and 6 directly above it from the seventh row. When we add 15 and 6 together (15 + 6), we get 21.

 

So the completed Pascal's Triangle would be:

                    1

            ...