Let pen's cost be x and pencil's cost be y.
6x + 5y = 2.50
3x + 2y = 1.15
Thus, 3x = 1.15 - 2y
Therefore, 6x = 2.30 - 4y
Substituting the value of 6x ;
(2.30 - 4y) + 5y = 2.50
or, 2.30 + y = 2.50
=> y = 0.20.
Substituting the value of y ;
6x = 2.30 - 4(0.20)
6x = 2.30 - 0.80 = 1.5
6x = 1.5
=> x = 0.25
Thus, 1 pen costs 0.25 $ and 1 pencil costs 0.20$.
Thus, cost of one pen is 0.25$.
Cost of 4 pencils is 0.80 $
0.25$ + 0.80$ = 1.05$
