How to do this?

If the younger brother does x questions per minute, then the elder brother will do the questions every minute.

then there is 7* (the sign is multiplied).

x=30

That is, the younger brother does 30 questions per minute, and the elder brother does 45 questions per minute.

Solve with equations.

Solution: Set: The elder brother does x dao every minute, and the younger brother does y dao every minute.

From the meaning of the title, it can be seen:

7x+8y=555

2x=3y.

x=30y=20

Answer...

Set: Brother X questions per minute.

Brother per minute y questions.

7x+8y=555

2x=3y.

x=30y=20

Set the elder brother to count x questions per minute and the younger brother to calculate y questions per minute.

then 7x+8y=555 (1).

2x=3y （2）

1) Formula multiplied by 2 (2) Formula multiplied by 7 finished.

14x+16y=1110

14x=21y

Calculate y=30 x=45

Answer: The elder brother does 45 oral calculations per minute, and the younger brother does 30 oral calculations per minute.

Let the elder brother do the x tract every minute, and the younger brother do the y tract every minute.

7x+8y=555

2x=3y, x=3 2y

Substituting 7x+8y=555, you can get, y=30, x=45Answer: The elder brother does 45 questions per minute, and the younger brother does 30 questions per minute.

Brother x per minute

Brother per minute y

7x+8y=5552x=3y

x=30y=20

The elder brother does 45 questions per minute, and the younger brother does 30 questions per minute.

Let's say: The elder brother does the title x every minute, and the younger brother does the title y every minute.

Solution: 2x=3y,7x+8y=555, x=,convert x to y,(7*,,,y=30,x=45

It's so hard.,This.。。 That one.. Alas.. I flash.

You divide the formula with ABC on the right.

The denominator is x2 (x-1).

The numerator is ax(x-1) + b(x-1) + cx2 = the molecule on the left = 2x2 + x-11

Then calculate the equation with ABC, ax(x-1)+b(x-1)+cx2=ax2-ax+bx-b+cx2=(a+c)x2+(b-a)x-b

So a+c=2, b-a=1, b=11

So a+b+c=a+c+b=2+11=13

The numbers in the million and 100,000 digits are 3 times the single digit, then the good bold digits in the single digit cannot be greater than 3 (if it is greater than 3, the 3 multiples will have two digits), and the maximum is 3. Another single-digit friend returns to the town to be 3 times the highest digit, then the highest digit can only be 1, and the rest of the digits are 0. So it's 19000093

The million mu spike and ten Xun Xiang numbers are 3 times the number of one digit, and the single digit number is 3 times the highest number, obviously the million digit number is 9 times the highest (that is, 10 million) number, only 1 and 9 meet the conditions, and the 8 digits of the family should be 19000093

lety=1/x

lim(x->∞x.sin(e (1 x) -1) = lim(y->0) sin(e y -1) y (0 0 numerator denominator derivative).

lim(y->0) e^ -1)=1

After the general fraction, the equivalence is replaced by the infinitesimal of the equivalence, and the molecule x -sin(x)cos x

dao x -x (1 - x 2) x specialization 4 o(x 4), denominator x sin(x) x *x x 4, so the limit is 1.