Answer:
I collect 4 rocks and 16 fossils. While my friend collects 12 rocks and 8 fossils.
Step-by-step explanation:
The number of total objects collected by me  = 20
The number of objects collected by my friend  = 20
Let us assume:
The number of rocks collected by me  = m
The number of fossils collected by me  = 2 k
⇒ m +  2 k =  20  .... (1)
So, according to the question:
The number of rocks collected by my friend = 3 x (rocks collected by me)  
 = 3 x (m)  = 3 m
The number of fossils collected by my friend = 1/2 x (fossils collected by me)    = 1/2 x (2k )  = k
⇒ 3 m +   k =  20  .... (2)
Solving (1)and (2) for the value of m and k, we get:
 m +  2 k =  20     ⇒ m = 20 - 2 k ... Put this in (2)
 3 m +   k =  20  ⇒  3 (20 - 2 k) +  k = 20
 ⇒ 60 - 6 k +  k  = 20
or, - 5k = -40
or, k = 40/5  = 8
⇒ k= 8
m + 2(8)  = 20
or, m = 4
Hence, the number of rocks collected by me  = m = 4
The number of fossils collected by me  =  2 k = 2 (4)  = 16
Hence, the number of rocks collected by my friend   = 3 m  = 3 x 4 = 12
The number of fossils collected by my friend   =   k =  8
Hence, I collect 4 rocks and 16 fossils. While my friend collects 12 rocks and 8 fossils.