https://www.delftstack.com/zh-tw/tutorial/python-3-basic-tutorial/python-while-loop/#while-%E8%BF%B4%E5%9C%88%E7%A4%BA%E4%BE%8B
請參考之後自己嘗試
關鍵字：python whle 累加

sum = 0
avg = 0
cnt = 0
n = int(input("Enter a number (-1 to end):"))

while n!=-1:
    cnt = cnt+1
    sum = sum+n
    n = int(input("Enter a number (-1 to end):"))

avg=sum/cnt
print('sum=',sum,'average=',avg)

total = 0
avg = 0
i = 0

score = input("請依序輸入成績(空格分開): ")
score_list = list(map(float, score.split(' '))) # 將成績轉成列表

Len = len(score_list) # 成績數量
while i < Len:
    total += score_list[i] # 總分

avg = total / Len # 平均

print("總分={:.2f} 平均={:.2f}".format(total, avg)) # 取自小數點第2位

順便附上不用While用法:

total = 0
avg = 0

score = input("請依序輸入成績(空格分開): ")
score_list = list(map(float, score.split(' '))) # 將成績轉成列表

total = sum(score_list) # 總分
avg = total / len(score_list) # 平均

print("總分={:.2f} 平均={:.2f}".format(total, avg)) # 取自小數點第2位

參考看看相關教學 ^_^
https://steam.oxxostudio.tw/category/python/example/sum.html

times_count = 0
total = 0

while True:
    n = int(input("請輸入分數，輸入'-1'結束填入 => "))
    if n == -1:
        break
    else:
        total += n
        times_count += 1

print("總分 =>",float(total),"\t平均 =>",total/times_count)

float(total) 只是為了要符合你總分使用浮點數的需求，可選擇要不要轉型。

☑用while迴圈
☑四科分數加總
☑四科分數平均

do_your_homework_by_yourself = True
while do_your_homework_by_yourself:
    my_scores = [78, 65, 91, 53]
    my_sum = sum(my_scores)
    my_avg = my_sum / len(my_scores)
    print(
        f"""分數：{my_scores[0]}
分數：{my_scores[1]}
分數：{my_scores[2]}
分數：{my_scores[3]}
總分={my_sum} 平均={my_avg}"""
    )
    do_your_homework_by_yourself = False