For this, we need to know subtraction. Since Ms Bright had 10 bananas, and a student took 5 of those, she now doesnt have those 5 bananas anymore. We need to calculcate how many she does have by subtracting what the student took from what Ms Bright had.
10 - 5 = 5 (since we know 5+5=10)
So, she now has 5 bananas.