Question 1
A Magic Grid of Integers
A grid containing some numbers is given below. Follow the steps as shown until no number is left.
When there are no more unstruck numbers, stop. Multiply the circled numbers. An example is shown below.


We need to follow the given rules to select numbers. Then we will multiply all the selected numbers.
Step 1 — Understanding the Game Rules
Let us understand how to play this game. First, we circle any number in the grid. Then, we strike out its row and its column. Next, we circle any unstruck number. We repeat striking out its row and column. We continue until all numbers are struck out. Finally, we multiply all the circled numbers.
Step 2 — Following the Example Rounds
The example shows us how to play. In Round 1, the number -6 is circled. Its row (Row 1) and column (Column 4) are struck out. In Round 2, the number 14 is circled. Its row (Row 2) and column (Column 2) are struck out. In Round 3, the number 20 is circled. Its row (Row 4) and column (Column 1) are struck out. In Round 4, the number 18 is circled. Its row (Row 3) and column (Column 3) are struck out. Now, all numbers are struck out.

Step 3 — Listing the Circled Numbers
From the example, we can see the circled numbers. The first circled number is -6. The second circled number is 14. The third circled number is 20. The fourth circled number is 18. These are the numbers we need to multiply.
Step 4 — Multiplying the Circled Numbers
We will multiply the four circled numbers. The numbers are -6, 14, 20, and 18. Let us multiply them step by step.
First, multiply -6 by 14.
Next, multiply -84 by 20.
Finally, multiply -1680 by 18.
Answer
(i) The final product of the circled numbers is -30240.
More questions in A
A Magic Grid of Integers
A grid containing some numbers is given below. Follow the steps as shown until no number is left.
When there are no more unstruck numbers, stop. Multiply the circled numbers. An example is shown below.
Try again, and choose different numbers this time. What product did you get? Was it different from the first time? Try a few more times with different numbers!
Play the same game with the grid below. What answer do you get?
What is so special about these grids? Is the magic in the numbers or the way they are arranged or both? Can you make more such grids?