Step 2: Determine the Square RootIgnore the last two digits of the number called out by the spectator and choose the memorised square which is just lower (or equal) to the remaining number. The corresponding square root is the first digit. of your answer
Now consider the last digit of the number called out by the spectator. If this is 0 or 5, then you immediately know that the last digit of your answer is also 0 or 5.
In all other cases, the last digit of the number called out will indicate two possible values for the last digit of the square root. For example, if the last digit is 9, then the square root may end in either 3 or 7.
To determine whether the lower or higher value should be taken, multiply the first digit of your answer by one greater than itself. If this is greater than the first part of the number called by the spectator (i.e., ignoring the last two digits), then the last digit of your answer is the lower of the two possible values. Otherwise the last digit is the higher value.
For example if the number called is 2809, the square root could be either 53 or 57. Since 5 x 6 = 30, and 28 is less than 30, the answer is 53.
Examples
Spectator Calls | Ignore Last 2 |
Lower Square | First Digit (a) | Last Digit |
a(a+1) | Square Root | 144 | 1 | 1 | 1 |
2 or 8 | 2 | 12 | 784 | 7 | 4 | 2 | 2 or 8 | 6 | 28 | 1369 | 13 |
9 | 3 | 3 or 7 | 12 | 37 | 2401 | 24 | 16 | 4 | 1 or 9 | 20 | 49 |
2809 | 28 | 25 | 5 | 3 or 7 | 30 | 53 | 3600 | 36 | 36 | 6 | 0 |
| 60 | 5041 | 50 | 49 | 7 | 1 or 9 | 56 | 71 | 7396 | 73 |
64 | 8 | 4 or 6 | 72 | 86 | 8836 | 88 | 81 | 9 | 4 or 6 | 90 | 94 | |