How to do page 88 of supplementary exercises in Volume 1 of fifth grade mathematics of Jiangsu Education Press?

How to do page 88 of supplementary exercises in Volume 1 of fifth grade mathematics of Jiangsu Education Press?

4. Party A and Party B walk from place a to place B at the same time. When Party A walks 1 / 4 of the whole journey, Party B is 640 meters away from place B. when Party A walks the remaining 5 / 6, Party B walks 7 / 10 of the whole journey. What is the distance between two places?
The remaining 1-1 / 4 is 3 / 4
So the remaining 5 / 6 is 3 / 4 × 5 / 6 = 5 / 8
At this time, a total of 1 / 4 + 5 / 8 = 7 / 8
Then the distance ratio of Party A and Party B is 7 / 8:7 / 10 = 5:4
So when a takes 1 / 4 of the whole journey, B takes 1 / 4 × 4 / 5 of the whole journey = 1 / 5
Then AB distance = 640 / (1-1 / 5) = 800 meters
5. Car a and car B leave from a and B at the same time, facing each other. Car a travels 75 kilometers per hour, while car B takes 7 hours to complete the whole journey. After 3 hours, the distance between the two cars is 15 kilometers. How many kilometers is the distance between a and B?
One situation: Party A and Party B have not met yet
Car B runs 3 / 7 of the whole journey in 3 hours
A 3-hour travel 75 × 3 = 225 km
AB distance = (225 + 15) / (1-3 / 7) = 240 / (4 / 7) = 420 km
One situation: Party A and Party B have met
(225-15) / (1-3 / 7) = 210 / (4 / 7) = 367.5km
6. A, already two people want to walk this road, a wants to walk 30 minutes, has to walk 20 minutes, walk 3 minutes later, a found something did not take, take things delay 3 minutes, a walk a few minutes to meet with B?
A starts 3 + 3 + 3 = 9 minutes later than B
Consider the whole distance as unit 1
So the velocity of a is 1 / 30
Speed of B = 1 / 20
When a finished taking things and set out, B had already gone 1 / 20 × 9 = 9 / 20
Then the distance between a and B is 1-9 / 20 = 11 / 20
The speed sum of a and B = 1 / 20 + 1 / 30 = 1 / 12
Then (11 / 20) / (1 / 12) = 6.6 minutes
reference resources

If a and B are opposite to each other, what is the algebraic formula seven thirds a + seven thirds B-5

-5

If the square of a is 18, then the square of 0.5A = ()

a*a=18
0.5a*0.5a
=0.25*(a*a)
Because a * a = 18
So 0.5A * 0.5A = 0.25 * 18 = 4.5

The area of a triangle is equal to the area of a circle with a radius of 10 cm. It is known that the height of a triangle is 8 cm. How many cm is the bottom of the triangle? (square)

10*10*3.14=8*t/2
t=200*3.14/8
T = 78.5 cm

X-2 / 5x + 4 = 3x-6 / 4x-8 and then subtract one

X-2 / 5x + 4 = 3x-6 / 4x-8, then subtract one and multiply by 3 (X-2)
3(5x+4)=4x-8-3(x-2)
15x+12=4x-8-3x+6
15x+12=x-2
14x=-14
x=-1

The perimeter of a semicircle flowerbed is 61.68 meters. How many square meters is its area?
The result of my calculation is:
∵d∏+d×1=61.68m
3.14+1=4.14
61.68 △ 4.14 = 14.8985 (5 cycles)!
Back: 14.8985 (5 cycles) × 3.14 = 696.9672 (what cycle)
It is conceivable that it is wrong to seek a positive solution
I've worked it out. I remember as soon as I wrote it out

Half circle is half circle. Divide 61.68 by paijia2, that is, 5.14, and get 12 as radius. Then use the formula to calculate the area. Note that the circumference of half circle is paijia2 and multiply by 2, so divide 61.68 by paijia2

Simple operation of 16 × (37 + 12)
It must be simple

16×(37+12)
=16×49
=16×（50-1）
=16×50-16×1
=800-16
=784

In equilateral triangle ABC, points D and E are on sides BC and AC respectively, and | BC | = 1 / 3 | BC |, | CE | = 1 / 3 | Ca |, ad and be intersect
=In the equilateral triangle ABC, the points D.E. are on the sides BC and AC respectively, and | BD | = 1 / 3 | BC |, | CE | = 1 / 3 | Ca |, ad and be intersect at the point P. Verification: AP vertical CP

What's the problem?

Let vector group A1, A2, A3 be linearly independent, and vector group B1 = a1 + A2 + a3, B2 = a1 + 2a2-a3, B3 = a1-a2 + 2A3, prove that B1, B2, B3 are linearly independent

Let k1b1 + k2b2 + k3b3 = 0, and then substitute B1 = a1 + A2 + a3, and sort it out to prove that K1, K2 and K3 are all 0

The top and bottom of the trapezoid are 2 and 8 respectively, and the two diagonals are 6 and 8
There should be a calculation process

It's 24
If in trapezoidal ABCD, ad is the upper bottom, BC is the lower bottom, AC, BD are diagonal, ad = 2, BC = 8, ad = 6, BD = 8, find s trapezoidal ABCD
If D is used as the extension line of de ∥ AC to BC and E is used as the extension line of BC, then ∥ aced is obtained, so CE = ad = 2, de = AC = 6
Let d be DF ⊥ BC over F, and CF = x, then BF = 8-x, EF = 2 + X
Then BD & sup2; - BF & sup2; = DF & sup2; = de & sup2; - EF & sup2;
So 8 & sup2; - (8-x) & sup2; = 6 & sup2; - (2 + x) & sup2;
The solution is x = 1.6
Because DF & sup2; = de & sup2; - EF & sup2;
So DF & sup2; = 6 & sup2; - (2 + 1.6) & sup2;
So DF = 4.8
So s trapezoid ABCD = 1 / 2 × (AD + BC) × DF = 24