Solution:
The sum of parents' ages is X, the sum of children's ages is Y, and there are n children.
X=6Y
(X-4)= 10(Y-n*2)
6Y-4= 10Y-20N
4Y=20N-4
Y=5N- 1
(X+ 12)=3(Y+n*6)
6Y+ 12=3Y+ 18N
3Y= 18N- 12
Y=6N-4
6N-4=5N- 1
N=3
I have three children.
8. Party A and Party B set out from A and B at the same time, and the place where they first met was 50 kilometers away from the midpoint. After arriving at B and A, Party A and Party B immediately turned around and walked back. So, Party A and Party B met for the second time at a distance of A 100 meters to find the distance between A and B..
Two people, A and B, set out from A to B, A can't, B rides a bike. If a walks 6 kilometers, they will arrive at b at the same time after 45 minutes from b; If A takes the poem of 1 first, and B catches up with A half an hour after departure, find the distance between A and B. ..
Let the speed of a be a km/h and the speed of b be b km/h.
45 minutes =3/4 hours
6+3/4a=3/4b
a=(b-a)x 1/2
simplify
b-a=8( 1)
3a=b(2)
( 1)+(2)
2a=8
A=4 km/h
B = 3x4 =12km/h
AB distance = 12x 3/4 = 9 km.
9. The factory is connected with A and B by road and railway. The factory bought a batch of raw materials with a price of 65,438+0,000 yuan a ton from Party A and transported them back to the factory, and made products with a price of 8,000 yuan a ton to Party B. It is known that the road freight rate is 1.5 yuan/(ton km), and the railway freight rate is 1.2 yuan/(ton km). There are two kinds of transportation. What is the sales amount of this batch of products relative to the sum of raw material expenses and transportation expenses?
10, Dong Zhang went to the department store to buy two types of envelopes, 30 of which were * * *, of which 1 yuan 50 cents was used to buy type A envelopes and 1 yuan 50 cents was used to buy type B envelopes, and each type B envelope was 2 points cheaper than type A envelopes. What is the unit price of these two kinds of envelopes?
Solution: If the unit price of type A envelope is A, the unit price of type B envelope is a-2.
If you buy a B-type A envelope, you will buy a 30-b-type B envelope.
1 yuan.50 = 150.
ab= 150( 1)
(a-2)(30-b)= 150(2)
By (2)
30a-60-ab+2b= 150
Substitution (1)
30a- 150+2b=2 10
30a+2b=360
15a+b= 180
b= 180- 15a
Replace (1)
a( 180- 15a)= 150
Answer? - 12a+ 10=0
(a-6)？ =36- 10
a-6= √26
a=6 √26
A 1≈ 1 1 min, then the b-type envelope 1 1-2=9 points.
A2≈0.9, then 0.9-2=- 1. 1 of the type B envelope is irrelevant, so it is discarded.
The unit price of type A is 1 1, and that of type B is 9.