the awnser to your question is 40 percent because sense a percentage means per one hundred and sense the denominator in 4/10 is 10 that means that it will be per one hundred and sense the numerator in 4/10 is 4 then that means that 4/10 is equal to 40 percent and also in order for out to get 40 percent you just have to add a zero to the numerator and the denominator.
