Answer :
so 1 minute to gather
1 minute per problem
so assumming the gathering time is included
1+1timesnumberofproblems=20
subtract 1 from both sides
1timesnumberofproblems=19
numberofproblems=19
he has 19 problems
1 minute per problem
so assumming the gathering time is included
1+1timesnumberofproblems=20
subtract 1 from both sides
1timesnumberofproblems=19
numberofproblems=19
he has 19 problems