THE EFFECT

The performer begins by placing a folded paper on the table, stating that it contains a prediction of a future event. They invite the audience to assist with the demonstration and ask anyone interested to open their phone's calculator app to follow along.

The performer then introduces their phones digital assistant (without saying her name to avoid triggering the audience's devices) and explains that she, along with the audience, will create something truly remarkable. Alternating between the digital assistant and members of the audience, the performer gathers five completely random five-digit numbers. Each number is entered by participants into their calculators.

Once all five numbers have been provided, everyone presses the "equals" button to reveal the grand total. The performer double-checks the total and confirms that the calculated sum matches their own.

Finally, the performer opens the sealed prediction, which has been in full view the entire time. The prediction matches the calculated total perfectly, leaving the audience in awe!

THE SECRET

BACKGROUND

This effect is based on a mathematical principle popularized by Martin Gardner, a legendary figure in recreational mathematics and magic. Gardner’s work often appeared in his Mathematical Games column in Scientific American (A | B). His contributions to magic and mathematics have inspired countless effects like this one. A full description of this trick, originally called "Predicting a Sum," can be found in his book Mathematics, Magic and Mystery, originally published in 1956 by Dover Publications.

The core of this trick relies on a simple mathematical adjustment: if the performer knows the first five-digit number, they can create a six-digit prediction by placing the digit "2" at the front of the number and subtracting "2" from the last digit (the "ones" place). This clever manipulation ensures the final sum matches the prediction. For example, if the first number is 31559 the prediction would be 231557.  After a spectator gives a random five-digit number, the next number provided needs to be the difference of each digit of the spectator's number, subtracted from the number nine. So if the spectator says 12345, the next number needs to be 87654.

THE METHOD

In this modern version, much of the work is streamlined using iPhone shortcuts. Here’s how it’s done:

PREPARATION AND INSTALLATION

There are two shortcuts that you’ll need to install on your iPhone:

Make sure you have read and completed the iOS Pre-Requisites.

In order for these shortcuts to run, you need to have an additional app installed called Actions. This app expands the capabilities of your shortcuts by providing additional actions. To find and install the Actions app, follow these steps:

• Open the App Store: Launch the App Store on your iPhone.

• Search for Actions: In the search bar, type "Actions" and look for the app developed by Sindre Sorhus.

• Download and Install: Tap the download button to install the app on your device.

• Launch the App: After installation, open the Actions app to ensure it is properly set up.

Restart Your Device: To make the actions show up in the Shortcuts app, restart your device after launching the Actions app.

ACTIONS APP

In order for these shortcuts to run, you need to have an additional app installed called Actions. This app expands the capabilities of your shortcuts by providing additional actions. To find and install the Actions app, follow these steps:

• Open the App Store: Launch the App Store on your iPhone.

• Search for Actions: In the search bar, type "Actions" and look for the app developed by Sindre Sorhus.

• Download and Install: Tap the download button to install the app on your device.

• Launch the App: After installation, open the Actions app to ensure it is properly set up.

• Restart Your Device: To make the actions show up in the Shortcuts app, restart your device after launching the Actions app.

PERFORMANCE STEPS

• Begin by running the "Number Prediction" shortcut. It will generate the prediction number, which you write down and place on the table. (To start, select RANDOM when the shortcut runs, followed by PREDICTION.  This gives you the number that you will use as the prediction.)

• During the performance, ask Siri to "Tell Me a Random Five-Digit Number." It will provide the key number you need to arrive at the prediction. Enter this number into your calculator and press the "+" button.

• Next, ask a spectator for a random five-digit number. Enter it into your calculator, but before pressing "+," show the calculator to the audience to verify the number. When you turn the phone back to yourself, tap the equation at the top of the screen and select "Copy" to save it to the clipboard. Then press "+" to continue.

• Repeat this process, alternating between asking your digital assistant and spectators for five-digit numbers. Each time a spectator provides a number, copy the equation to the clipboard before pressing "+".

• The "Tell Me a Random Five-Digit Number" shortcut uses the clipboard equation to calculate the next number your assistant provides. After a spectator gives a random five-digit number, the next number provided by your digital assistant will be the difference of each digit subtracted from the number nine. This ensures the final sum will always match the prediction.

THE REVEAL

• Once all five numbers are entered, everyone presses "=" to reveal the total. The performer confirms the total matches their own calculator and then opens the sealed prediction, revealing a perfect match.

ALTERNATE OPTIONS FOR THE NUMBER PREDICTION

When running the Number Prediction Shortcut, there are a few alternate options available aside from the RANDOM > PREDICTION choice already explained. These options provide additional flexibility and enhance the performance of your effect: