Answer: There are 15 friends.
Explanation:
We know that there is N friends (N is the number that we are looking for)
Each friend weights 1/20 ton.
Now, the weight of the N friends together is N times 1/20 ton.
Then we have:
N*(1/20) ton = 3/4 ton
We solve this for N.
First multiply both sides by 20.
20*N*(1/20) = N = 20*(3/4) = 60/4 = 15