Answer :

Given,
Sn = 280, n = 4 and common difference is -20.


Let the first term be a.


Since the sum of n terms is
Sn =


Where,


a = First term of AP
d = Common difference of AP
and no of terms is ‘n’



So sum of 4 terms S4
]
280 = 2× [2a + 3 × (-20)]
140 = 2a – 60
2a = 140 + 60
2a = 200
a = 100


a1 = a = 100
a2 = a1 + d = 100 - 20 = 80
a3 = a2 + d = 80 - 20 = 60
a4 = a3 + d = 60 - 20 = 40


Hence, The value of prizes are 100, 80, 60 and 40.


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