Goldenrod and No Hope are in a horse race with 6 contestants. How many different arrangements of finishes are there if No Hope always finishes before Goldenrod and if all of the horses finish the race?

Question

নিচের অপশন গুলা দেখুন

• 720
• 360
• 120
• 640

Answer 1

সঠিক উত্তর হচ্ছে: 360

ব্যাখ্যা:

Two horses A and B, in a race of 6 horses... A has to finish before B

 

if A finishes 1... B could be in any of other 5 positions in 5 ways and other horses finish in 4! Ways, so total ways 5*4!

 

if A finishes 2... B could be in any of the last 4 positions in 4 ways. But the other positions could be filled in 4! ways, so the total ways 4*4!

 

if A finishes 3rd... B could be in any of last 3 positions in 3 ways, but the other positions could be filled in 4! ways, so total ways 3*4!

 

if A finishes 4th... B could be in any of last 2 positions in 2 ways, but the other positions could be filled in 4! ways, so total ways... 2 * 4! 

 

if A finishes 5th .. B has to be 6th and the top 4 positions could be filled in 4! ways..

 

A cannot finish 6th, since he has to be ahead of B

 

Therefore total number of ways = 5*4! + 4*4! + 3*4! + 2*4! + 4! = 120 + 96 + 72 + 48 + 24 = 360