Answer:
4
Step-by-step explanation:
If she got a 90% on her test, and the test was 40 questions long, we need to do a bit of division and multiplication.
We have to divide 40 by 100, as percentages are out of 100.
So now we have 0.4.
Now we multiply this by 90.
36. She got 36 answers correct out of 40, which means she got four wrong.