50% of boys in a class is equal to 80% of girls, so whose number is more?

50% of boys in a class is equal to 80% of girls, so whose number is more?

More boys
If the number of boys is x and the number of girls is y, then
1/2X＝4/5Y,X/Y＝8/5＝1.6
So the number of boys is 1.6 times that of girls, so there are more boys

If M is a rational number, then a. | m | B. | M2 C. | M2 + 1 does not necessarily have an arithmetic square root in the following numbers
If M is a rational number, then the following numbers do not necessarily have the square root of arithmetic
A.|m| B.㎡ C.㎡+1 D.m+10

D. Because the other three are all nonnegative

The sum of the three numbers of a, B and C is 180. The number of a is three times of the number of B, and the number of B is two times of the number of C. what are the solutions of the equations of the three numbers of a, B and C

The number C is x, the number B is 2x, and the number a is 6x
x+2x+6x=180
x=20
A is 120, B is 40, C is 20

1： If a is greater than B and a is less than 0, then a + B? A must be negative, B may be negative, C may be positive and D may be 0

A

The average number of a, B and C is 70, the ratio of a to B is 5:2, and the ratio of B to C is 4:7. What are the three numbers of a, B and C?

Let three numbers of a, B and C be x, y and Z, then (x + y + Z) / 3 = 70, 2x = 5Y and 7Y = 4Z. By solving this system of linear equations of three variables, x = 100, y = 40 and z = 70 are obtained

If there is a real number x satisfying cosx - Sin ^ 2x = a, what is the value range of real number a?

A:
a=cosx-(sinx)^2
=cosx-[1-(cosx)^2]
=(cosx)^2+cosx-1
=(cosx+1/2)^2-5/4.
x∈R,cosx∈[-1,1],
So the value range of a is [- 5 / 4,1]

20.4 × (7 / 2-5) + 47.9 × 3 / 5 + 60% × 31.7

20.4 × (7 / 2-5) + 47.9 × 3 / 5 + 60% × 31.7
=4 × 3 / 5 + 47.9 × 3 / 5 + 3 / 5 × 31.7
=(20.4 + 47.9 + 31.7) × 3 / 5
=8 × 3 / 5
=61.08

The linear equations AX = B, where x is n. the necessary and sufficient condition for a vector to have infinite solutions is?

When the rank of the coefficient matrix is equal to the rank of the augmented matrix, the equations have solutions. When the rank of the two matrices are both N, the equations have unique solutions. When the rank of the two matrices is equal and less than N, the equations have innumerable solutions

Party A and Party B work together to process a batch of parts, and they can complete the task in 12 days. It is known that the work efficiency ratio of Party A and Party B is 3:4
How many days will it take to complete the task if the parts are processed by Party A alone

The cooperation between Party A and Party B is completed every day
1 △ 12 = 1 / 12
A finish every day
1 in 12 × (3 + 4) 3 = 1 in 28
A separate processing, to complete
1 / 28 = 28 days

Solving equation 8x ^ 2 - (2x-3) (4x + 2) = 14

8x²-8x²+8x+6=14
8x=8
x=1