Answer: let a be X.
B is X-3.
X*7=(X-3)*9-3
X= 15
2. In quadrilateral ABCD, angle B is 70, angle C is 90, BC=CD, AB=AD, and how many degrees is angle A?
Answer: The drawing shows that angle B is equal to angle D, so angle A is 360-90-2*70= 130.
It takes 6 hours for Party A to do a job alone, and 4 hours for Party B to do a job alone. After A finishes 1/3, how many hours will they need to cooperate?
Solution: Let the total workload be 1, and A has already completed 1/3, so there are still 2/3 unfinished.
The work efficiency of Party A is 1/6, and that of Party B is 1/4. Two people work together.
The efficiency is1/6+1/4 = 5/12, so the remaining 2/3 needs to be completed.
(2/3)/(5/12) = (2/3) * (12/5) = 8/5 =1.6 (hour).
For this kind of problem, we only need to understand the relationship between the following three quantities: total workload Q and work efficiency. ※
Rate η, working time t: q = η t, (equivalent to S=Vt in the distance problem)
η=Q/t，t=Q/η。 In calculation, the total workload is often set to 1.
4. The number of boys in Class 6 (1) last semester was 5/3 of that of girls, and two girls were transferred this semester. Now the number of boys in Class 6 (1) is 3/2 of that of girls. How many boys were there in Class Six (1) last semester?
Solution: Suppose there were X boys and 3x/5 girls last semester, then there is an equation:
x \u( 3x/5+2)= 3 \u 2
That is 2x=3(3x/5+2).
10x=3(3x+ 10)
X=30, which means there are 30 boys.
The fruit shop brought in a batch of fruits, accounting for 5/8 of the total, and then 700 Jin. Now the fruit in the fruit shop is exactly 2/3 of the original. How many kilograms did the fruit shop have?
Solution: Let the original fruit be x kg, and there is an equation according to the meaning of the question:
( 1-5/8)x+700=2x/3
3x/8+700=2x/3
9x+ 16800= 16x
7x= 16800
∴ x = 16800/7 = 2400kg
That is, the original fruit is 2400 Jin.
6. Xiaoming's age this year is 2/7 of his father's age and 5/ 16 of his mother's age. His father has always been three years older than his mother. How old is Xiaoming this year?
Solution: Suppose Xiaoming is X years old, then Xiaoming's father is 7x/2 years old and Xiaoming's mother is 16x/5 years old.
Then the equation 7x/2- 16x/5=3.
That is, 35x-32x=30
3x=30
X = 10 years old.
That is, Xiaoming 10 years old.
7. Each internal angle of a regular polygon is 20 greater than its adjacent complementary angle. What is the sum of the internal angles of this polygon?
Answer: The complementary angle of the inner angle is (180-20)/4=40, so the inner angle 140 is a positive nonagon.
The sum of internal angles is 140*9= 1260.
8. If the minimum internal angle of a polygon is 120 and slightly larger than its internal angle is 125, then each internal angle is 5 times larger than the previous internal angle, and the ratio of the maximum internal angle to the minimum internal angle is 4: 3. How to find the number of sides and the degree of the maximum internal angle of this polygon?
Answer: The maximum internal angle is 120/3*4= 160.
The number of edges is (160-120)/5+1= 9.
9. Party A needs 65,438+00 hours, Party B needs 65,438+02 hours and Party C needs 65,438+05 hours to move the goods in the warehouse. There are the same warehouses A and B. Party A is in warehouse A, and Party B is moving goods at the same time. At first, Party C helped Party B to move the goods, but in the middle, it turned to Party A.. All the goods in the last two warehouses were handled at the same time, and Party C helped Party A and Party B respectively.
Solution: Because warehouse A and warehouse B are the same, and because warehouse A needs 10 hour to move.
B needs 12 hour, and C needs 15 hour.
It is known that the total workload of warehouse A is the least common multiple of 10, 12 and 15.
[ 10, 12, 15]=60
So A is 6 per hour, B is 5 per hour and C is 4 per hour.
So the total workload of warehouses A and B is 60×2= 120.
To do it at the same time, all three people should do it.
120 ÷ (6+5+4) = 8 hours
So c is like a gang.
(60-6× 8) ÷ 4 = 3 hours
Such as c and B.
(60-5×8)4 = 5 hours
10. The cost of commodity A is 80% of the price, the price of commodity B is 275 yuan, and the cost is 220 yuan. Now the store sells one commodity A and two commodities B together at 90% of the sum of their prices. So this set can be profitable. What is the cost of commodity A in 80 yuan?
Solution: suppose the price of commodity A is X.
(x+2*275)*0.9-0.8x-220*2=80
(x+550)*0.9-0.8x-440=80
0.9x+495-0.8x-440=80
0. 1x+45=80
0. 1x=80-45
X=250
250*0.8=200
A: The cost of commodity A is 200.