Given
Last team received $40,000.
Champion team received $65,000.
Award increases by $2500 for the successive finishing places.
Prizes received by the teams in increasing order are, $40,000, $42500, $4500, $47500,
This is an A.P. with a = 40,000, d = 2500 and I = 65,000
Let the number of terms be n. Then,
an = 65000
a + (n − 1)d = 65000
⇒ 40000 + (n − 1) × 2500 = 65000
⇒ (n − 1) × 2500 = 65000 − 40000
⇒ (n − 1) = 25000/2500
⇒ n − 1 = 10
⇒ n = 10 + 1
n = 11
∴ 11 teams participated in Football World Cup.
Hence, the correct answer is 11.