Not adjusting after calculation
"The Unadjusted Answer"
The Mistake in Action
Calculate $(4 \times 10^5) \times (5 \times 10^3)$. Give your answer in standard form.
Wrong: $4 \times 5 = 20$ $10^5 \times 10^3 = 10^8$ Answer: $20 \times 10^8$
Why It Happens
Students correctly multiply the numbers and add the powers, but forget that the final answer must also be in standard form — with A between 1 and 10.
The Fix
After calculating, check if A is still between 1 and 10. If not, adjust.
$20 \times 10^8$ is not in standard form because $20 \geq 10$.
Adjust: $20 = 2 \times 10^1$
So: $20 \times 10^8 = 2 \times 10^1 \times 10^8 = 2 \times 10^9$
Answer: $2 \times 10^9$
Spot the Mistake
Can you identify where this student went wrong?
$(4 \times 10^5) \times (5 \times 10^3)$
$= 20 \times 10^8$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: