#22
Top 50 Mistake
Dividing the wrong way round
"The Fraction Flip"
The Mistake in Action
Make $v$ the subject of $t = \frac{d}{v}$
Wrong: $tv = d$ $v = td$
Why It Happens
Students correctly multiply both sides by $v$ but then don't complete the rearrangement properly. They multiply again instead of dividing.
The Fix
$$t = \frac{d}{v}$$
Step 1: Multiply both sides by $v$: $$tv = d$$
Step 2: Divide both sides by $t$: $$v = \frac{d}{t}$$
Think of it like this: If $t = \frac{d}{v}$, then $v = \frac{d}{t}$ (the non-subject swaps position).
Spot the Mistake
Can you identify where this student went wrong?
Make $v$ the subject of $t = \frac{d}{v}$
Multiply both sides by $v$: $tv = d$
$v = td$
Click on the line that contains the error.
Related Topics
Learn more about the underlying maths: