Treating truncation the same as rounding H
"The Truncation Trap"
The Mistake in Action
A number is truncated to 3.4 (1 d.p.). Write the error interval.
Wrong: $3.35 \leq x < 3.45$
Why It Happens
Students apply rounding rules, forgetting that truncation just "chops off" digits without considering what comes next.
The Fix
Truncation means cutting off – the number could have been anything from 3.4 up to (but not including) 3.5.
For truncation to 3.4:
- Lower bound: 3.4 (could be exactly 3.4)
- Upper bound: 3.5 (3.49999... would truncate to 3.4)
Error interval: $3.4 \leq x < 3.5$
Key difference:
- Rounding to 3.4: $3.35 \leq x < 3.45$
- Truncating to 3.4: $3.4 \leq x < 3.5$
Spot the Mistake
Can you identify where this student went wrong?
Truncated to 3.4
$3.35 \leq x < 3.45$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: