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Mother gave Honghong some money to buy new year cards. There are three kinds of New Year cards: A, B and C. each kind of card is 0.50 yuan and each kind of card is 1.20 yuan? How much is the B card?
1.20:0.5 = 12:5, 8 + 6 = 14 sheets, 14 ^ (1-512), = 14 ^ 712, 14 × 127, = 24 sheets; 24 × 0.5 = 12 yuan, 12 ^ (24-8) = 12 ^ (16, = 0.75 yuan), a: mother gives Honghong 12 yuan, B card 0.75 yuan each
How to really understand and master the proportion method to solve practical problems
To master the proportion method to solve practical problems, we should understand the relationship between various quantities
Basic formula: distance = speed × time; distance △ time = speed; distance △ speed = time
A certain distance, time and speed are inversely proportional
Speed is constant, distance is proportional to time
Time is fixed, distance is proportional to speed
Workload = work efficiency × work time;
Working time = workload △ work efficiency;
Work efficiency = workload △ time required
Taking the travel problem as an example, we can see the application of proportion
Xiaohua from a to B, one-third riding, two-thirds by car; from b back to a, three-fifths riding, two fifths by car, the result is half an hour slow, known, riding 12 kilometers per hour, 30 kilometers per hour by car, ask: how many kilometers between a and B?
Consider the whole distance as unit 1
The distance difference between the two rides is 3 / 5-1 / 3 = 4 / 15
Speed ratio of riding and cycling = distance ratio = 30:12 = 5:2
Then the ratio of time is 2:5
So it takes two fifths of the time to ride
So the time taken to complete 4 / 15 of the whole journey by bike = (1 / 2) / (1-2 / 5) = 5 / 6 hours
So the time to complete the whole ride = (5 / 6) / (4 / 15) = 75 / 24 hours
Then the whole journey = 12 × 75 / 24 = 37.5km
123. It takes three hours for Xiaoqiang to ride a bicycle from place a to place B. if he walks two kilometers first, and the speed of walking is one third of that of riding a bicycle, then he arrives 20 minutes later. How many kilometers are there between a and B?
20 minutes = 1 / 3 hour
Walking and cycling speed ratio = 1 / 3:1 = 1:3
Time ratio = 3:1
2 km walking time = (1 / 3) / (1-1 / 3) = 1 / 2 hours
Walking speed = 2 / (1 / 2) = 4 km / h
Cycling speed = 4 × 3 = 12 km / h
Distance between a and B = 12 × 3 = 36 km
124. The distance between a and B is 20km. After a starts from a and travels to B for 30 minutes, B starts from B and drives to a at a speed twice as fast as a per hour. The two cars meet at C, 12km away from B. what's the speed of a and B?
Speed ratio = distance ratio = 1:2
If line B is 12 km, then line a is 12 / 2 = 6 km
So a 30 minutes = 1 / 2 hour, 20-12-6 = 2km
Speed of a = 2 / (1 / 2) = 4 km / h
Speed of B = 4 × 2 = 8 km / h
A mathematical score calculation problem~~
The title is 1 / 1 × 2 + 1 / 2 × 3 + 1 / 3 × 4 +. + 1 / 49 × 50
How to calculate? Don't just write the answer, the steps are listed ~ ~ thank you
The original equation can be changed to (1-1 / 2) + (1 / 2-1 / 3) + (1 / 3-1 / 4) + +（1/49-1/50）
1-1 / 2 + 1 / 2-1 / 3 + 1 / 3-1 / 4 + 1 / 4 + +1/49-1/50
Except the first and last two numbers are offset, so 1-1 / 50 = 49 / 50
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