Question

Solve the pair of linear equation 3p+5q=21 and 2p+q=7 by substitution method also find the value of 5p-3q.

Answer 1

the given system of equation is:-
3p+5q=21 --1
2p+q=7 --2

1 can also be written as:-
3p+5q=21
3p=21-5q
p=(21-5q)/3 ---3

Put value of p in 2
2((21-5p)/3)+q=7
(42-10q+3q)/3=7
42-7q=7.3
42-7q=21
-7q=21-42
-7q=-21
7q=21
q=21/7
q=3

put value of q in 3

p=(21-5.3)/3
p=(21-15)/3
p=6/3
p=2

hence, q=3 and p=2.

put value of p and q in 5p-3q

=5.2-3.3
=10-9
=1