According to the meaning of the question, there are 3 trees in each row, and it seems that it takes 30 trees to plant 10 row. However, there are only nine trees now. So at least plant some trees (mathematically called key points) at the intersection of several rows. To this end, we can design six three points (three lines intersect) and three four points (four lines intersect).
A tree is eight meters high. A person climbs four meters every minute and drops three meters. How many minutes does it take him to reach the top of the tree?
(8-4)/(4-3)+ 1=5
Grandpa said to Xiaojun, "I am seven times your age now, six times your age in a few years, five times, four times, three times and two times your age in a few years." How old are Grandpa and Xiaojun now?
Grandpa said to Xiaojun, "I am seven times your age now."
So grandpa's age now is a multiple of 7.
Consider a multiple of 7 within 100, as follows
7 14 2 1 28 35 42 49 56 63 70 77 84 9 1 98
Because this is a practical problem.
Grandpa's age is five figures: 56 63 70 77 84.
Then the corresponding age of Xiaojun is 8 9101112.
Grandpa, it's been x years, six times bigger than Xiaojun.
The column equation (8+x)*6=56+x is not an integer, so the answer that Xiaojun is 8 years old is excluded.
The column equation (9+x)*6=63+x is not an integer, so Xiaojun is 9 years old.
The column equation (10+x)*6=70+x is solved with x=2, and the answer of Xiaojun 10 can be considered.
The column equation (1 1+x)*6=84+x is not an integer, so the answer of Xiaojun 1 1 year is excluded.
In fact, as long as grandpa's age is MINUS 6 times that of Xiaojun, 10 times, the conditions will be met.
So now we have the answer. Xiaojun 10 years old, grandpa is 70 years old.
Then we will verify the known conditions.
Grandpa, who has been for X years, is five times as old as Xiaojun.
Solve the column equation (10+x)*5=70+x to get x=5.
Grandpa, it's been x years, four times bigger than Xiaojun.
Solve the column equation (10+x)*4=70+x to get x= 10.
Grandpa, it's been x years, three times bigger than Xiaojun.
Solve the column equation (10+x)*3=70+x to get x=20.
Grandpa, it's been x years, twice as big as Xiaojun.
Solve the column equation (10+x)*2=70+x to get x=50.
Final answer
Grandpa is now 70 years old and Xiaojun 10 years old.
Grandpa's age is six times that of Xiaojun in two years.
Grandpa is five times as old as Xiaojun in five years.
After 10, grandpa's age is four times that of Xiaojun.
Twenty years later, grandpa is three times as old as Xiaojun.
Grandpa is twice as old as Xiaojun at 50.
There are still a few that can't be pulled down. See for yourself.
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