if you substitute this into the other equation that you are given it looks like this 8(326-S)+5S=1972. After this we use PEMDAS to solve for S 2608-8S+5S=1972 2608-3S=1972 -3S=(-636) -S=(-212) S=212 If we know S=212 we can go back and solve the origonal equation for A. A+212=326 A=114
We know that The formula for combinations is C=n!/[(n-r)!*r!] where n is the total number of objects you choose from r is the number that you choose to arrange
in this problem n=15 students r=4 students C=15!/[(15-4)!*4!]-----> C=15!/[11!*4!]---> (15*14*13*12*11!)/(11!*4*3*2*1) C=(15*14*13*12)/(24)----->C=1365
