Its same as powers of a whole number.
Lets take example
(1/2)²=1/2×1/2=1/4
We can write it in a different way (0.5)²=0.5×0.5=0.25
In the science class,
there are 3 girls and 1 boy (grade 7)
and 5 girls and 5 boys (grade 8)
There is a total of 14 pupils being 8 girls and 6 boys
The probability of choosing a boy will be

Which can be simplified into

by
dividing 2 from the numerator as well as the denominator.
There are 14 total cards and you need NOT yellow so it would be
8/14 which can be reduced to 4/7