Let the cost of 1 pen and 1 pencil are Rs.x and Rs.y respectively.
Then as per the question
5x + 8y = 120 …….(i)
8x + 5y = 153 …….(ii)
Adding (i) and (ii), we get
13x + 13y = 273
⇒ x + y = 21 …….(iii)
Subtracting (i) from (ii), we get
3x – 3y = 33
⇒ x – y = 11 ………(iv)
Now, adding (iii) and (iv), we get
2x = 32
⇒ x = 16
Substituting x = 16 in (iii), we have
16 + y = 21
⇒ y = 5
Hence, the cost of 1 pen and 1 pencil are respectively Rs.16 and Rs.5.