A and B go to the library to borrow books. A goes every four days, B goes every five days. If they meet in the library on July 20, they will go to the library at the same time next time

A and B go to the library to borrow books. A goes every four days, B goes every five days. If they meet in the library on July 20, they will go to the library at the same time next time

4. The least common multiple of 5 is 20
That is to say, they met again in the library 20 days later
20 days after 20 July, it should be 9 August
The next time they are in the library at the same time is August 9

A, B and C are friends. They go to the library every other day. A goes to the library every three days, B goes every four days and C goes every five days. One day, the three of them just meet in the library. How many more days will they meet in the library?

Because 3, 4 and 5 are mutually prime, their least common multiple is the product of 3, 4 and 5, so the least common multiple of 3, 4 and 5 is 3 × 4 × 5 = 60, that is, the minimum interval between meeting in the library is 60 days. A: at least meet again in the library in 60 days

Each of the three friends goes to the library every other day. Once every three days in a, once every four days in B, and once every five days in C. the last time they met in the library was on Tuesday. What day was the next time they met in the library?

【3,4,5】=60 60/7=8…… 4 2 + 4 = 6 meet on Saturday
I can't guarantee it's right

33 math problem. Urgent
To understand the service life of a batch of light bulbs, take ten light bulbs out of them. In this question, what is the individual?

The life of a light bulb

If A3 = 3 / 2 and S3 = 9 / 2, then q =?

a3=a1q^2=3/2,
S3=a1+a1q+a1q^2=9/2,
Divide by (1 + Q + Q ^ 2) / Q ^ 2 = 3,
∴2q^2-q-1=0,
Q = 1, or q = - 1 / 2

12 times 3 / 4 - 1 / 9. It's easy to calculate

12 times 3 / 4 - 1 / 9
=9-1/9
=Eight and eight out of nine

Let a, B, C and d be rational numbers, we define a new operation, | ABCD | = ad BC, then when | 32 (x-1) 4 | = 16, we try to find the value of X

|3 2（x-1) 4|=16
3*4-2*(x-1)=16
2(x-1)=12-16
2(x-1)=-4
x-1=-2
x=-1

How many proportions can you make up according to 4.8x2.5 = 1.2x10? Write it out

This formula is just like a × B = C × D. [a = 4.8, B = 2.5, C = 1.2, d = 10]
It can be composed of:
a:c=d:b
b:c=d:a
a:d=c:b
b:d=c:a
Four basic proportional expressions
also:
a: B = CD: B (2), etc
(2) is the square of 2

Given the line segment AB, take a point C on the extension line of Ba so that Ca = 3AB, then the ratio of the line segment CA to the line segment CB is ()
A. 3：4B. 2：3C. 3：5D. 1：2

As shown in the figure above, ∵ CA = 3AB ∵ CB = Ca + AB = 4AB ∵ CA: CB = 3:4

Two times of a three digit 3AB equals ab8. Find the three digit

3AB can be regarded as 300 + ab
Ab8 can be seen as 10 times AB plus 8
The equation can be listed as follows:
（300+ab）×2=10×ab+8
2×ab+600=10×ab+8
8×ab=592
ab=74
So this three digit number is 374