What are the formulas of fourth grade mathematics?

The circumference of a rectangle = (length+width) ×2

，C=(a+b)×2

Circumference of a square = side length ×4,

C=4a

Area of rectangle = length × width

，S=ab

Area of a square = side length × side length

S=a.a= a^2

Area of triangle = base × height ÷2

，S=ah÷2

Area of parallelogram = base × height,

S = ah

Trapezoidal area = (upper bottom+lower bottom) × height ÷2,

S=(a+b)h÷2

Circumference = π× diameter = π× radius× 2,

c=πd =2πr

Area of circle = π× radius× radius πr

10.

Surface area of cylinder: the surface area of cylinder is equal to the perimeter of the bottom multiplied by the height plus the area of the circles at both ends. Formula: S=ch+2s=ch+2πr2.

1 1.

Law of fractional addition and subtraction: Fractions with the same denominator are added and subtracted, only the numerator is added and subtracted, and the denominator remains unchanged. Fractions of different denominators are added and subtracted, first divided, then added and subtracted.

12.

The multiplication of fractions is: use the product of molecules as numerator and the product of denominator as denominator. The law of division of fractions: dividing by a number is equal to multiplying the reciprocal of this number.

13.

Speed × time = distance, distance/speed = time, distance/time = speed.

14.

Unit price × quantity = total price, total price/unit price = quantity, total price/quantity = unit price.

15.

Work efficiency × working hours = total workload, total workload ÷ work efficiency = working hours, and total working hours = working efficiency.

16.

Additive commutative law: Two numbers are added to exchange the position of the addend, and the sum remains the same.

17.

Law of addition and association: When three numbers are added, the first two numbers are added first, or the last two numbers are added first, and then they are the same as the first number.

Three numbers add up, and the sum remains the same.

18.

Multiplication and exchange law: when two numbers are multiplied, the position of the exchange factor and the product remain unchanged.

19.

Multiplication and association law: when three numbers are multiplied, the first two numbers are multiplied, or the second two numbers are multiplied first, and then the third number is multiplied, and the product remains unchanged.

20.

Multiplication and distribution law: when two numbers are multiplied by the same number, you can multiply the two addends by this number respectively, and then add the two products, and the result is unchanged. Such as: (2+4) × 5 = 2× 5+4× 5. 6. Nature of division: In division, the dividend and divisor are expanded (or reduced) by the same multiple at the same time, and the quotient remains unchanged. Divide 0 by any number other than 0 to get 0.

2 1.

The basic property of the equation is 1: both sides of the equation add or subtract the same number at the same time, and the equation still holds.

22.

Basic property 2 of the equation: When both sides of the equation are multiplied (or divided) by the same number at the same time, the equation still holds.

23.

Meeting distance = speed x meeting time,

Meet time = meet distance ÷ speed and,

Speed Sum = Meeting Distance/Meeting Time

24.

Catch-up distance = speed difference × catch-up time,

Catch-up time = catch-up distance ÷ speed difference,

Speed difference = catching distance ÷ catching time

25.

Downstream velocity = still water velocity+water velocity,

Countercurrent velocity = still water velocity-water flow velocity,

Still water velocity = (downstream velocity+countercurrent velocity) ÷2