Science and technology books are 5 more than story books, and story books are 1 / 3 less than science and technology books. How many science and technology books are there? Write down the process

Science and technology books are 5 more than story books, and story books are 1 / 3 less than science and technology books. How many science and technology books are there? Write down the process

Suppose x books of science and technology and Y books of stories, then according to the meaning of the title: X-Y = 5, y = x (1-1 / 3) = 2x / 3, the above two expressions are combined, and the solution is x = 15, y = 10

A story book has 45 pages, 5 pages less than 1 / 2 of a science and technology book. How many pages is this science and technology book

Pages of science and technology books
=(45 + 5) △ 1 / 2
=50×2
=100 pages

There are 270 science and technology books in the library, four fifths more than story books. How many story books are there

270 / (1 + 4 / 5) = 150

Two cars set out from a certain place at the same time to transport a batch of goods to the construction site 165 kilometers away. Car a arrived 48 minutes earlier than car B. when car a arrived, car B was 24 kilometers away from the construction site. How many hours did car a spend on the whole journey?

48 minutes = 0.8 hours; 24 △ 0.8 = 30 (km / h); 165 △ 30-0.8, = 5.5-0.8, = 4.7 hours; a: it took 4.7 hours for car a to complete the whole journey

40% of 20 is (), 10% of 36 is (), 60% of 50 kg is (), 25% of 800 m is (), 30% more than 50 kg () () 30% less than 12 m

40% of 20 is (8), 10% of 36 is (3.6), 60% of 50 kg is (30 kg), 25% of 800 m is (200 m), 30% more than 50 kg (65 kg) (8.4 m) and 30% less than 12 M. the first one on the first floor is wrong

The speed of train is 60% faster than that of car. How much slower is the speed of car than that of train?

6 = 37.5% a: the speed of a car is 37.5% slower than that of a train

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 drives from a to B at the speed of 40 km / h, and travels 60 km / h when it returns from the original road
We need formulas, not equations, but ideas

Assuming that the one-way distance is 1, then the time from a to B is 1 / 40, and the time from a to B is 1 / 60
Average speed of round trip = total distance △ total time
（1+1）÷（1/40+1/60）
=2÷1/24
=48 (km)
A: the average speed of this car is 48 kilometers per hour

If (1 / 2a-x) ^ 2 = 1 / 4A ^ 2 + 1 / 2ay + 1 / 9, then the values of X and y are

(1/2a)^2+x^2-ax=1/4a^2+1/2ay+1/9
1/4a^2+x^2-ax=1/4a^2+1/2ay+1/9
x^2-ax=1/2ay+1/9
X = 1 / 3 or - 1 / 3
Y2 / 3 or - 2 / 3
What a coincidence, it's you again

The road between a and B is 375 km long. A car has driven 150 km from a to B in the first two hours. At this speed, how many hours will it take to reach B?

A: it will take another 2 hours to get to B