Let the amount for first prize = Rs x
number of prizes = 7
Total prize amount = Rs 700
Therefore, the series of 7 prizes are as follows:
(x) + (x – 20) + (x – 40) + (x – 60) + (x – 80) + (x – 100) + (x – 120) = 700
⇒ 7x – 420 = 700
⇒ 7x = 1120
⇒ x = 1120/7 = 160
Hence, the seven prizes are Rs 160, Rs 140, Rs 120, Rs 100, Rs 80, Rs 60 and Rs 40.