Elementary Mathematics Application Questions One Question with Process Question 5

The dog runs 3 steps and the fox runs 5 steps, that is, the speed of the fox is 3 5 of the dog.

The dog runs 4 steps away from the fox and runs 7 steps, that is, the distance of the fox is 4 7 of the dog.

Velocity is the distance traveled per unit of time, so if the speed of the dog is s meters and seconds, then the speed of the fox is (5 3 * 4 7) s meters and seconds, which is (20 21) * s meters and seconds.

Suppose the dog catches up with the fox after the dog runs for t seconds, then the distance the fox runs is 30+dt*s-(20 21)*s*t=30

s*t=630

So, the dog had to run another 630 meters to catch the fox.

Pay attention to the "time.""、"Distance"

In the same time, the fox runs 5 steps and the dog runs 3 steps, and the dog's stride length is 7 4 times longer than that of the fox.

Therefore, in the same time, the distance that the dog runs is equivalent to 3*7 4 = 21 4 steps of the fox.

Their distance ratio is 21 4 5 = 21 20 When the dog catches up with the fox, the dog runs 21 parts of the distance and the fox runs 20 parts, and their difference is 30 meters, so the dog has to run 21 * 30 = 630 meters to catch up with the fox.

I can provide a question where the known number a is divided by 3 and left for 2, divided by 4 for 2, divided by 7 for 2, divided by 7 for 4.

It is known that the number b is divided by 7 and left with 2, divided by 8 and left with 2, divided by 5 and left with 3.

It is known that the number c is divided by 13 to balance 3, divided by 7 to balance 1, divided by 19 to balance 6.

What is the abc of each? What is its greatest common factor?

a=74b=58

c = 120 greatest common factor = 2

Solution: From the title, there are 64 25%=16 black rabbits, and 64-16=38 white rabbits.

Set to buy black rabbit x only, then.

x+16) (x+64) 100%=40% gives x=16

A: I bought another 16 black rabbits.

Arithmetic method:

It turned out that the black rabbit accounted for 1 4 of the total and was 16 individuals.

Then, the white rabbit accounts for 3 4 of the total and is 48 individuals.

After buying some black rabbits, black rabbits account for 2 5 of the total, then, white rabbits account for 3 5 of the total, because there is no white rabbit to buy, so, the number of white rabbits has not changed, so, 48 corresponds to 3 5, then, now there are a total of 48 3 5 = 80, 80-64 = 16. So, I bought 16 black rabbits.

The law of the equation is like "zhenxiai168" said, there used to be a black rabbit = 64 * 25% = 16, let the buy x black rabbit, there is (16 + x) (64 + x) = 40%.

Solution x=16

In the past, Black Rabbit = 64 * 25% = 16, set to buy x Black Rabbit, there is (16 + x) (64 + X) = 40%

Solution x=16

Black rabbits have 64 25%=16, white rabbits 64 75%=48, after buying black rabbits, black rabbits account for 40% but the number of white rabbits has not changed, that is, white rabbits account for 60%, so after buying black rabbits, there are a total of 48 60%=80, so black rabbits have 80-48=32, so buy 32-16=16 black rabbits.

Kids, this question is not difficult at all.

Set and buy the black rabbit x and get:

16+x) (64+x)*100%=40% Find x=16