Rounding, estimating and converting units

In short: In everyday life a good approximation is often enough. Rounding, estimating and converting units reliably prevent mistakes and bad purchases.

In more detail: When rounding, look at the first digit left out: from 5 it is rounded up.

In detail

• Rounding: 3.46 to one decimal = 3.5; to a whole number = 3.
• Estimating: 19.90 · 4 ≈ 20 · 4 = 80; this is how to check results.
• Order of magnitude: Check plausibility: is the result even possible?
• Length: 1 km = 1000 m; 1 m = 100 cm; 1 cm = 10 mm.
• Weight: 1 kg = 1000 g; 1 t = 1000 kg.
• Volume: 1 l = 1000 ml; 1 l = 1 dm³.
• Time: Hours and minutes: 1.5 h = 1 h 30 min (not 1 h 50 min).
• Data: 1 GB = 1000 MB (decimal) or 1 GiB = 1024 MiB (bruchrechnung-grundlagen).