Question

if 5x + 7y = 21 and 7x + 5y = 15, then find the value of x + y ​

Answer 1

5x+7y=21

5x=21-7y

x=(21-7y)/5

subsituting value of x in equation 7x+5y=15

7(21 - 7y) / 5 +5 y=15

(147 - 49y)/ 5 + 5y = 15

147/5 - 49y/5 +5y = 15

147/5 - 15 +5y -49y/5 = 0

72/5 -(24/5) y = 0

72/5 = (24/5) y

y=72/24

y=3

susituting in equation 7x+5y=15

7x+5(3) = 15

7x=15-15

7x= 0

x=0

so, finally

x+y=3+0=3

may be this is your answer..........

hope it helps you