Xiaolan's watch is three minutes fast and Xiaojun's watch is three minutes slow. They all arrive at school at 7:30 by their own watch. Who will arrive first?

Xiaolan's watch is three minutes fast and Xiaojun's watch is three minutes slow. They all arrive at school at 7:30 by their own watch. Who will arrive first?

Xiaolan, because when Xiaolan's watch shows 7:30, it's actually 7:27. When Xiaojun's watch shows 7:30, it's already 7:33

Xiao Ming and Li Li go to school from home. Xiao Li has to walk 1 / 5 more than Xiao Ming. Li Ming takes 1 / 7 less time than Xiao Li. What is the speed ratio between Xiao Li and Li Ming?

Xiao Li has to walk 1 / 5 more than Xiao Ming, so Xiao Ming's journey is 1, and Xiao Li's is 1 + 1 / 5 = 6 / 5
Li Ming spent 1 / 7 less time than Xiao Li, so Xiao Li spent 1 time, Xiao Ming spent 1-1 / 7 = 6 / 7
Therefore, the speed ratio of Xiaoli and Xiaoming is as follows:
(6/5÷1):(1÷6/7)
=6/5:7/6
=36:35

From school to bookstore, it takes Xiaoming 10 minutes and Xiaoli 8 minutes. The simplest speed ratio between Xiaoming and Xiaoli is ()

Four to five

If f (x) is a decreasing function on R, and the image of F (x) passes through points a (0,1) and B (3, - 1), the inequality | f (x + 1) is obtained|

First draw a sketch, you can directly draw a graph of the function, for example, draw a diagonal line through a (0,1) and B (3, - 1). If the absolute value of Y coordinates is between - 1 and 1, the corresponding value range of X is between 0 and 3. Therefore, if x + 1 is between 0 and 3, you can solve this inequality

In the equation AX ^ 2 + BX + C = 0 (a is not equal to 0), if a + B + C = 0, then one root of the equation must be ()

b=-a-c
Then ax & # 178; - ax CX + C = 0
ax(x-1)-c(x-1)=0
(x-1)(ax-c)=0
So one is x = 1

A classroom's electric energy meter has the word "220V 5A", physics! Mainly for electric energy! Thank you!
The electric energy meter of a classroom has the words "220 V 5A", the maximum current allowed to pass is () a; 10 fluorescent lamps with "220 V 40 W" are installed in the classroom. If the lamp is turned on less than 1 hour every day, the electricity consumption per month (20 days) can save () J electric energy?
The second question to write, tell me the idea or process, thank you!

5
W=Pt=10*40W*3600s*20=400*20*60*60=8000*3600=2.88*10^7J

Using Cauchy's mean value theorem to determine the positive and negative solution of function derivative: Let f (0) = 0, f (x) monotonically increase on (0, + ∞). It is proved that f (x) x monotonically increase on (0, + ∞)

According to the known condition f (0) = 0, f (x) increases monotonically on (0, + ∞)
Know: F (x) > = 0, f '(x) > = 0
And [f (x) x] '= f' (x) x + F (x) > = 0
So f (x) x increases monotonically on (0, + ∞)
It is almost obvious that we don't know what to do with the mean value theorem

The name plate of Xiaoming household appliance rice cooker is marked with the word of 220V 1100W, and the name plate of electric kettle is marked with the word of 220V 550W
If one time is during the peak period of electricity consumption, these two kinds of electrical appliances in his home are in use at the same time, it can be estimated that the actual working voltage at this time is 200V. If it takes 10 minutes to cook and boil water, then they consume electricity_____ J. Not only the answer, but also the way to think about it

The formula w = P real T, where t is 10 minutes, and the actual total power P real, P real = P real 1 + P real 2, P real 1 = u real & # 178 / R1, P real 2 = u real & # 178 / R2, where u real is 200V, and R1, R2, R1 and R2 can be calculated according to the words of 220V 1100W, 220V 550W on the nameplate, and the formula is p = u & # 178 / R, where p is 1100W, 550W, and u is 220V
So far, all the physical quantities to be used have been found and can be substituted into the formula
The above is the process of thinking, starting from seeking knowledge and pushing it all the way to conditions
When writing, just turn it upside down, from the condition (known) to the end of seeking (knowledge)

x^2-5xy+6y^2=0,x^2+y^2=5

X = 2, y = 1. Ha ha, I guess these two as soon as I guess. It's really nice to bring them in

The power supply is 220 V and 60 W from a 220 V power supply to a lamp in a distant construction site
Due to the resistance of the wire, the actual power consumed by the bulb is 55W, so the electric power consumed by the wire?

The resistance of 220v60w bulb: r = u × U / P = 220 × 220 / 60 ≈ 806.7 (Ω) when the actual power consumed by the bulb is 55W, the voltage at both ends: u × u = P × r = 55 × 806.7 = 44368.5u ≈ 211 (V) when the actual power consumed by the bulb is 55W, the current passing through: I = P / u = 55 / 211 ≈ 0.26 (a) the electric power consumed by the conductor