 Hi, and how are you all today? I'm Priyanka. The question says, from a class of 25 students, 10 are to be chosen for an excursion party. There are three students who decide that either all of them will join or none of them will join. In how many ways can the excursion party be chosen? So here we need to find in how many ways the excursion party can be chosen. So there are, we are given a class of 25 students and 10 are to be right. Now here it can be done in two ways, that is way A and way B. Here there is three three particular students can go and then rest seven will be chosen out from, from remaining 22 students. Right, and there is way B in which three particular students are not chosen, chosen from remaining 22 students. Right, number of A ways A can be chosen is since three particular students are chosen there is only one combination possible here. The order of choosing the student does not matter. Whereas in this seven students can be taken out of 22 so the combination will be 22 C7. Right, plus here no student is selected, so there is no combination whereas 10 students are chosen from the batch of 22. So this is our total ways of choosing the excursion party that will be 22 C7 plus 22 C10 and this is our required. So just understand what is said in the question and see whether combination are possible or not possible and then proceed on. Take care.