In the 13th century, Italian mathematician Leonard raised the following interesting question: if each pair of big rabbits gives birth to a pair of little rabbits every month, and each pair of little rabbits becomes big rabbits after growing for a month, and all rabbits survive, how many pairs of little rabbits will there be after a year when someone raises a pair of newborn rabbits? It's better to have a formula. Why do you do it like this?

In the 13th century, Italian mathematician Leonard raised the following interesting question: if each pair of big rabbits gives birth to a pair of little rabbits every month, and each pair of little rabbits becomes big rabbits after growing for a month, and all rabbits survive, how many pairs of little rabbits will there be after a year when someone raises a pair of newborn rabbits? It's better to have a formula. Why do you do it like this?

The number of rabbits in each month was 1,1,2,3,5,8,13,21,34,55,89144
The beginning of the third month is the sum of the first two months

Today, my father's age is three times that of Xiaofang. A few years ago, my father's age was five times that of Xiaofang. A few years ago, my father's age was seven times that of Xiaofang. Their age difference is between 20 and 30. How old is my father this year?
The sooner the answer comes out, the better
.
Otherwise do not give points Oh

Let Xiaofang be x and dad be 3x
3X-a=5(x-a);
3x-b=7(x-b);
The results show that x = 2A, x = 1.5b
Because x is an integer, X is a multiple of 6
In addition, 3x-x = 2x is between 20 and 30, so x = 12
My father is 36 years old and Xiao Fang is 12 years old
Six years ago, my father was five times as old as Xiao Fang
Nine years ago, my father was seven times as old as Xiao Fang

The content is: ABCs
× 9
---------
scba
abcs
× 9
-------
scba

ABCD
× 9
DCBA
Because DCBA is still four digit
So a must be 1,
Otherwise ABCD × 9 will not be a four digit number
Because the number of D × 9 is 1,
So d must be 9
Write the formula as
1 BC9
× 9
9CB 1
Because B × 9 has no carry (otherwise a × 9 + carry product is not four digits)
So B must be 0 (because a = 1)
Because the number of C × 9 + 8 is 0,
So C must be 8
That is, ABCD = 1089
Checking calculation: 1089 × 9 = 9801

1. In order to solve the problem of fresh water shortage on the island, the soldiers of an island and the local residents jointly built a fresh water reservoir with a length of 22m, a width of 10m and a depth of 1.8m. How many cubic meters can the reservoir store at most?
This is question 15 of p55 in the math book
Math book p55 16 also help to solve the volume of a big ball
We need answers by 10 o'clock tonight

Vitamin · Luoluo Hello, my answer is as follows:
（1）22×10×1.8
=220×1.8
=396 (M3)
（2）
24ml=24cm 12ml=12cm
12-4=8cm (24-12)÷3=4cm