Explanation:

The total number of ways in which the horses can graze the grass of the field = 210

Step-by-step explanation:

The horses who entered the field : h1 , h2 , h3
Number of horses who entered the field = 3
The given portions into which the horses are made to enter : p1 , p2 , p3 , p4 , p5 , p6 , p7
Total number of portions = 7
So, we need to find the number of ways in which the horses are made to enter the 7 portions given that no two horses can enter the same portion
Now, h1 horse can graze the grass in 7 ways
Also, h2 can graze the grass in 6 ways
And, h3 can graze the grass in 5 ways.
So, Total number of ways = 7 × 6 × 5
Hence, The total number of ways in which the horses can graze the grass of the field = 210