The math problem in the first year of junior high school, I remembered 8 for a while, and it was dif

1. d2. c

3.c Let the top of these 4 numbers be n, then the sum of 4 numbers is.

n+(n+5)+(n+10)+(n+15)4n+30, so the sum of 4 numbers minus 30 must be divisible by 4, so choose c4The advance rate of degrees, minutes and seconds is 60

7.It took x hours to set it up.

10x+8）/12=x+1/6

Solve x=3

So the total distance is 10x=30km

A: A and B are 30 kilometers apart.

b correct. The imaginary segment 90° A (obtuse angle) 180° B (1 2 A) 90° (1 2 180°) is set as an acute angle.

The turn of 75 degrees is 10:30

Solution: Set the need for 10% concentration of brine x kg.

10%x+30%(250-x)=22%×250x=100

250-100 = 150 kg.

A: 100 kg of brine with 10% concentration and 150 kg of brine with 30% concentration are required.

Solution: Let the concentration of 10% x kg be required, and the concentration of 30% of the 250 x kg 10% x (250 x) 30% 250 22% will be multiplied by 100 on both sides.

10x＋（250－x）×30＝250×2210x－30x＋7500＝5500

20x＝2000

x 100 concentration of 30% to: 250 x 250 100 150

A: 100 kg of 100% brine is required 150 kg of 15% saline.

1.In 2010, there were x number of students enrolled in the vocational secondary school.

then there are (x = 20,000, 20,000 * people in 2011) = 10,000 people).

The subsidy is 1500 * 24000 = 36000000 (yuan) = 3600 (10,000 yuan) A: . In front of the dry sedan car...

2.Set a total of x

Then x-1 2x-1 2*1 2*x=15+1x=64Answer: There are 64 in total

3.Time = distance speed.

Derived from the title (hours).

A: After 1 hour.

4.Let the smallest date be x, then the three unclear ones are (x+1), (x+7), and (x+8).

There is x+(x+1)+(x+7)+(x+8)=52x=9 Answer: The date of one of the days is the 9th.

Substitute x=--2.

a=11/5

5a+x=13

x = is exponential) = m (2 is exponential).

That is, m(1 is an exponent) = 3y+1=(2 is an exponent) = 5y+33y+1=5y+3

y=-1, so fill -1 in parentheses

x=1-2m

3x+2m=6x-1

x=(2m+1)/3

x=1-2m=(2m+1)/3

The solution yields m=1 2

8.Let the purchase price be x

x=800 A sail collapse: the purchase price is 800 yuan.

I think it's right.

The armor setting speed is x

Then B 4 hours is 5 4

So in 2 hours A has 5 more than B 4

So 2(x-5) 5 4

x-5≥10

x 15A: A is riding at least 15 km/h.

B has advanced a total of 5*(4+2)=30 kilometers in the previous 4 hours, and A must ride at least 30 2=15 kilometers in order to catch up.

Solution: In ABC, ACB=90° A=45° ABC=45° extends the line A at the point D

then d (not quite correct, because it's hard to say) = 45°-15°=30° and a b

2= ACB=30° choose B

Because of the top angle, the little triangle on top, you just need to know the other corner, because it's parallel. Angle 2 can be subtracted by 18 and 90 by the angle just found.

Did you learn parallel in your first year of junior high school? Since 1 is equal to 2, then a is parallel to b (two straight lines parallel at the same angle of the same topic), so 4 is equal to. How to describe that is the adjacent complement angle of 3, you can set a 5) because 3 123°, so 5 is equal to 4 is equal to 57°.

I don't know if you understand.

7.Let cad= 3, c+ d+ 3=180 (meaning of the adjacent complement angle).

and c= d (known).

3 = c = d (property of the equation).

ab cd (known).

2 = d (two straight lines are parallel, and the inner wrong angles are equal).

c= d (sek).

2 = 3 (equal substitution).

1 + 2 + 3 = 180 (meaning of adjacent complement angle).

1 = 2 = 3 (property of the equation).

2 + 3 = FAD (known).

fad=2 2 (property of the equation).

AB bisector FAD (meaning of angular bisector).