PLS HELP ME

Question

Three school participated in a competition. There were a total of 25 projects summited by Sch B and C. If there were a total of 16 projects not from sch c and a total of 12 projects not from sch A,how many projects were submmited in total by the three schools?

Answer 1

NOTE:  This answer assumes that you meant to write: "a total of 25 projects submitted by schools A, B, and C" and "how many projects were submitted by each of the three schools?"

 

A + B + C = 25      (total,     eq1)
A + B = 16             (not from C,    eq2)
B + C = 12            (not from A,   eq3)

Plugging eq2 into eq1,     16 + C = 25
                                         C = 9          (subtract 16 from both sides)

Plugging C=9 into eq3:      B + 9 = 12
                                         B = 3             (subtract 9 from both sides)

Plugging B=3 into eq2:       A + 3 = 16
                                         A = 13          (subtract 3 from both sides)
Checking:
     Is   13 + 3 + 9 = 25  ?    yes.