Core Speed Shortcut
Multiplying by 5 (Append 0 & Halve)
To multiply by 5 quickly in your head, do not do long multiplication. Instead, use the fact that 5 = 10 / 2. Divide the number by 2 (halve it), then multiply by 10 (append 0 or shift decimal).
Mathematical Symmetry & Identity
$$N \times 5 = \frac{N \times 10}{2} = \frac{N}{2} \times 10$$
Visual Mental Pipeline
Step-by-Step Execution Rules
- 1 For even numbers: Cut the number in half, then append a 0. Example: 48 × 5 → Half of 48 is 24 → Append 0 = 240.
- 2 For odd numbers: Cut the number in half (which ends in .5), then drop the decimal point. Example: 37 × 5 → Half of 37 is 18.5 → Shift decimal = 185.
- 3 For 3-digit numbers: Break into easy chunks (e.g. 146 × 5 → Half of 140 is 70, half of 6 is 3 → 73 → 730).
Worked Examples & Thought Process
48 × 5
Example 1
Step 1: Half of 48 = 24
Step 2: Append 0 → 240
= 240
76 × 5
Example 2
Step 1: Half of 76 = 38
Step 2: Append 0 → 380
= 380
37 × 5
Example 3
Step 1: Half of 37 = 18.5
Step 2: Shift decimal → 185
= 185
124 × 5
Example 4
Step 1: Half of 124 = 62
Step 2: Append 0 → 620
= 620
Ready to Hone Your Speed?
Put this shortcut into practice with 10 procedural, timed questions. Sharpen your reaction time and track your accuracy.