2 / 5 of a number is 60. What's 20% of the number\

2 / 5 of a number is 60. What's 20% of the number\

Let this number be X
x*2/5=60
x=150
So 150 * 20 / 100 = 30
The answer is 30

Three fourths of a number is more than 25% of 60. How much is this number? The comprehensive formula is urgent

（60×25%+3）÷3/4
=18÷3/4
=24

How many numbers appear simultaneously in the sequence 1,3,5,7,. 199519971999. And 1,4,7,10.199319961999?

At the same time, 6N + 1 appears
So the new sequence is 1, 7, 13 In 1999, there were 334

If the function y = f (x) has a continuous third derivative in a neighborhood of point x0, and the first and second derivatives of F (x) are 0, and the third derivative is not 0, then why is x0 not the extreme point of F (x)?

The Taylor expansion of F (x) is in the neighborhood of x0
y=f(x0)+f'(x0)(x-x0)+f"(x0)(x-x0)^2/2!+f"'(x0)(x-x0)^3/3!+.
Because f '(x0) = f "(x0) = 0, so
y=f(x0)+f"'(x0)(x-x0)^3/3!+.
When x = x0 + H, y-f (x0) ≈ F "'(x0) * H ^ 3 / 3!
When x = x0-h, y-f (x0) ≈ - F "'(x0) * H ^ 3 / 3!
Because F "'(x0) is not zero, the sign of y-f (x0) in the neighborhood of x0 is opposite, so f (x0) can not be the extreme point

Write the value of a in the calculated expression
int a = 4;
(A)a += (a++); (B) a += (++a) ;(C) (++a) += (a++);

(A)
A + = (a + +) is equivalent to
a=a+(a++)
=4+4
=8
Then execute a + +, a = 9
(B)
A + = (+ + a) is equivalent to
a=a+(++a)
=5+5
=10
(C)
(+ + a) + = (a + +) is equivalent to
++a=++a+a++
=5+5
=10
Then execute a + +, a = 11

The advantages and disadvantages of keeping pets!

Keeping Pets
Some people like keeping pets,while some people think we should stop keeping pets,but I think we shouldn’t stop keeping pets because pets are our good friends.For example,a strong dog can keep your house safe all the time and a lovely cat or rabbit can make you happy all the time.You will have fun when you play with them and look after them.When you feel sad,you can play with your pets and this will give you a good mood.But not all pets are good.Some dangerous and wild animals,such as snakes,wolves,tigers may be harmful to you.Sometimes ,pets will damage the enviroment because they always make dirty things.But ,on the whole, I think pets are friendly to people and we shouldn’t stop keeping pets.

What is the higher order infinitesimal of 1?

First of all, infinitesimal refers to the variable whose value is 0 when taking the limit. From infinitesimal, we can deduce the equivalent infinitesimal and the higher-order infinitesimal. The equivalent infinitesimal means that when two independent variables take the limit, the value is 0, but after they divide, the limit is 1

X times 2x times 3x = 30, how much is x equal to

2/1*2*3+2/2*3*4+2/3*4*5+…… +What is 2 / 28 * 29 * 30

First, write the general expression as follows:
1/(n*(n+1)*(n+2))
=1/2*{1/[n*(n+1)]-1/[(n+1)*(n+2)]}
Take n = 1 to 28, then sum and cancel the middle term,
The answer is:
1/2*（1/2－1/890）
=217/870

Prove the existence of sequence limit