If you want to add all the values of s1, you need to iterate over the values() of dictionary students.
students={
1: {"pup1": "001", "s1": 10, "s2": 20},
2: {"pup2": "124", "s1": 20, "s2": 30},
3: {"pup3": "125", "s1": 30, "s2": 40}}
sum1 = 0
for data in students.values():
sum1 += data['s1']
avg = sum1 / len(students)
print(sum1)
print(avg)
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solved how to add just the values in key s1 [closed]