Master Wang and master Li donated 200000 yuan in total, and Master Wang donated 3 / 4 more

Master Wang and master Li donated 200000 yuan in total, and Master Wang donated 3 / 4 more

If master Wang donates x 10000 copies, Master Li donates (1-0.75) x = 25X 10000 copies
x+0.25x=20
x=16
Master Li donated 20-16 = 40000 copies
A: Master Wang donated 160000 copies and master Li donated 40000 copies

Mr. Zhang and Mr. Li are 56 years old this year. A few years later, when Mr. Zhang reaches Mr. Li's age, the age ratio of Mr. Zhang and Mr. Li is 4:5. How old is Mr. Zhang?
Use formulas instead of equations

Suppose Mr. Zhang is x years old and Mr. Li is y years older than Mr. Zhang
2x+y=56
(x+y)/(x+2y)=4/5
Then x = 24
Mr. Zhang is 24 years old

A passenger train is 200 meters long and a freight train is 280 meters long. They run in parallel tracks. It takes 16 seconds from the meeting of the two cars' heads to the two cars' tailboxes. It is known that the speed ratio of the passenger train to the freight train is 3:2. How many meters do the two cars travel per second

Let a speed be 3x and B speed be 2x
16(3x+2x)=200+280
48x+32x=480
80x=480
x=6
6*3=18 6*2=12
A: speed a is 18m / h, speed B is 12m / h

The speed of the car is 40% slower than that of the train, and the speed of the train is several% faster than that of the car

Forty

It is known that: as shown in the figure, △ ABC, ab = AC, D is the point on BC, passing through point D, make de ‖ AB and intersect AC at point E

It is proved that: ∵ AB = AC, ∵ B = C. ∵ de ∥ AB, ∵ B = CDE. ∵ C = CDE

A car drove from a to B for 3 hours, 40 kilometers per hour, and returned from B to a for 60 kilometers per hour

40 × 3 = 120 km
120 △ 60 = 2 hours
Average round trip speed: 120 × 2 ÷ (3 + 2) = 48 km / h

X = 2A / 3, y = 2 + 4A / 1-2a, X is y

Because x = 2A / 3
So 2A = 3x
Because y = (2 + a) / (1-2a)
So substitute 2A = 3x into y = (2 + a) / (1-2a)
So y = (2 + 3x) / (1-3x)

A highway is 432km long, and a passenger car can complete the whole journey in 4.5 hours; a freight car can complete the whole journey in 5.4 hours. How fast is the speed of the passenger car faster than that of the freight car?

432 △ 4.5-432 △ 5.4 = 96-80 = 16 (km / h) a: the speed of a bus is 16 km / h faster than that of a truck

4. If the equation 4 ^ x-a * 2 ^ x + 4 = 0 of X has a real root in [0,2], find the value range of the real number a

4 ^ x-a * 2 ^ x + 4 = 0 has real roots in [0,2]
That is, there exists x ∈ [0,2] such that 4 ^ x-a * 2 ^ x + 4 = 0 holds
That is, a * 2 ^ x = 4 ^ x + 4
A = 2 ^ x + 4 / 2 ^ x holds
Let t = 2 ^ x, ∵ x ∈ [0,2] ∵ t ∈ [1,4]
∴y=2^x+4/2^x=t+4/t
y'=1-4/t²=(t²-4)/t²=(t+2)(t-2)/t²
1 ≤ T0, y decreasing
When t = 2, Ymin = 4
When t = 1 and T = 4, ymax = 5
The range of y = 2 ^ x + 4 / 2 ^ x = t + 4 / T is [1,5]
The range of a is [1,5]

There is a batch of cement in a construction site. My brother transported 40% in one day and 35% in the next. There are still 17 tons left. How many tons of cement are there

17 / (1-40% - 35%) = 68 (tons), that is 17 / (100-40-35) * 100 = 68