① According to "10 cows can eat for 20 days", it can be calculated that 10×20=200 cows can eat 1 day.

② According to "15 cows can eat 10 day", 15× 10= 150 cows can eat 1 day. This is because the grassland grass is short 10 days (20 days-10 days) and the number of cattle is 50 (200- 150). It can be seen that the grass growing every day can feed five cows (50÷ 10) 1 day.

(3) 1 day, how many cows can eat the original grass (excluding the newly grown grass)?

(10-5) × 20 = 5× 20 =100 (head)

Or: (15-5) ×10 =10 ×10 =100 (head)

Now there are 25 cows coming in, because the new grass on the grass is enough to raise 5 cows. Just calculate how many days the remaining 20 cows have eaten the original grass, and the result will come out.

100 ÷ (25-5) =100 ÷ 20 = 5 (days)

Only in this way can we get the answer step by step.

(1) How many cows can eat the new grass growing on the pasture every day;

( 10×20- 15× 10)÷(20- 10)

=(200- 150)÷ 10

=50÷ 10

=5 (head)

(2) 1 day How many cows have enough grass to eat?

(10-5) × 20 = 5× 20 =100 (head)

(3) How many days will it take to feed 25 cows with old grass and new grass on the pasture?

100 ÷ (25-5) =100 ÷ 20 = 5 (days)