#!/usr/bin/perl

use Data::Dumper;

my @students = qw {
  Thomas 60 10 20 85
  Samuel 35 90 80 65
  Adam   100 90 85 52
};

my %h;
while ( my ($student, @vals) = splice @students, 0, 5) {
  $h{$student} +=  @vals[$_] * (0.2, 0.25, 0.25, 0.3)[$_] for 0..3;
}

print Dumper \%h;