---
title: "Number Juggle 1"
id: 57023
type: "computer_media"
slug: "number-juggle-1"
url: "http://localhost/computer_media/number-juggle-1/"
markdown_url: "http://localhost/computer_media/number-juggle-1.md"
published_at: "2024-10-02T07:45:22+00:00"
modified_at: "2026-03-30T21:20:04+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/47_Num.png"
excerpt: "A number-guessing trick that walks the player through doubling, adding, and subtracting, then seemingly reads their mind to reveal the original number."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
genre:
  - name: "Game"
    slug: "game"
    taxonomy: "genre"
    url: "http://localhost/type/game/"
media_contents:
  - id: 56732
    title: "Timex Sinclair Public Domain Library Tape 1001"
    type: "computer_media"
    url: "http://localhost/computer_media/timex-sinclair-public-domain-library-tape-1001/"
media_type: "Program"
mediadate: "198x"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/47_Num.png"
media_type_tags: "Game"
---

# Number Juggle 1

This program is a classic “number mind-reading” trick that guides a player through a sequence of arithmetic operations and then reveals the number they originally thought of. The player is asked to think of a number, double it, add five, subtract seven, and enter the result; the program then recovers the original number using the inverse formula K = (A + 2) / 2. Input is collected via two INPUT statements: one for the player’s name (A$) and one for the computed result (A).

***

## Program Analysis

### Program Structure

The program follows a straightforward linear flow with no loops or subroutines. It can be divided into four phases:

1. **Introduction** (lines 10–40): Displays a title in inverse video, prompts for the player’s name, and stores it in `A$`.
2. **Instruction sequence** (lines 65–140): Uses `CLS` and `PAUSE 400` to pace three successive on-screen instructions — double it, add five, subtract seven — creating the illusion of a controlled, dramatic reveal.
3. **Calculation and reveal** (lines 145–185): Accepts the player’s result as `A`, computes the original number as `K`, and displays it.
4. **Save/auto-run footer** (lines 300–410): Stops normal execution, then saves the program with an auto-run flag, followed by `RUN` for re-entry.

### The Mathematics

The trick relies on a deterministic arithmetic chain. If the player’s secret number is *n*, the operations are:

- Double it: *2n*
- Add five: *2n + 5*
- Subtract seven: *2n + 5 − 7 = 2n − 2*

The player types *2n − 2* as `A`. The program then computes `K = (A + 2) / 2`, which simplifies to `(2n − 2 + 2) / 2 = n`, correctly recovering the original number.

### Key BASIC Idioms

Several idiomatic patterns appear throughout the listing:

- The title at line 10 is printed entirely in inverse video using `%`-escaped characters, a common technique for visual emphasis without machine code.
- `PAUSE 400` (approximately 16 seconds at 50 Hz) is used twice to give the player time to perform the mental arithmetic before the screen is cleared and the next instruction shown.
- Line 135 uses `A$;,,"SUBTRACT SEVEN"`, placing the instruction text in the third print zone by supplying two commas, creating an indented appearance for variety.
- Line 75 uses a leading comma (`,"DOUBLE IT"`) to push the text to the second print zone, adding visual alignment.

### Variable Usage

| Variable | Purpose |
| --- | --- |
| `A$` | Player’s name, used throughout for personalised prompts |
| `A` | The result entered by the player after completing the arithmetic |
| `K` | The recovered original number, computed as `(A+2)/2` |

### Notable Anomalies

Line numbering is irregular and non-sequential in places (10, 12, 30, 40, 65, 70, 75, 95, 100, …), suggesting the program was edited incrementally with lines inserted between existing ones. There are notable gaps — for instance between lines 185 and 300 — which may indicate deleted or planned content. The `STOP` at line 300 ensures that the `SAVE`/`RUN` block at lines 400–410 is only reached during tape saving, not during normal gameplay execution.

## Source Code

```
  10 PRINT "%N%U%M%B%E%R% %J%U%G%G%L%E"
  12 PRINT 
  30 PRINT "NAME OF PLAYER"
  40 INPUT A$
  65 CLS 
  70 PRINT A$;", THINK OF A NUMBER AND"
  75 PRINT ,"DOUBLE IT"
  95 PAUSE 400
 100 CLS 
 120 PRINT A$;",ADD FIVE"
 125 PAUSE 400
 130 CLS 
 135 PRINT A$;,,"SUBTRACT SEVEN"
 140 PRINT "AND TYPE IN THE RESULT"
 145 INPUT A
 150 CLS 
 175 LET K=(A+2)/2
 185 PRINT "YOUR NUMBER, ";A$,",WAS ";K
 300 STOP 
 400 SAVE "1004%7"
 410 RUN
```