1. The formula of this problem doesn't seem to work. . . There is a good way.

5/8= 1/2+ 1/8

And 2+8= 10.

So these two natural numbers are 2 and 8.

This topic can be regarded as five for boys and four for girls. In this way, there are 5-4 more boys than girls =1,and the total number of students is 5+4=9.

So there are more boys than girls 1/4× 100% = 25%.

Girls account for 4/9 of the total number.

3。 This is easy to say. Since this number is divided by 3.4.5, which is greater than 1, it is the common multiple of 3.4.5+1, which is the least common multiple of 3.4.5+1, that is, 6 1.

4。 This problem is definitely unsolvable.

You see

When Xiaohong is 3 years old, her father can be 30 years old and her grandfather can be 75 years old.

When Xiaohong 15 years old, her father can be 35 years old and her grandfather is 58 years old.

There are two completely different situations, and many others can be cited.

Maybe you have the wrong number. Go back and have a look, then I can add.

Supplement: The average age is 36, and the total age is 36×3= 108. According to the meaning of the question, Xiaohong's age is 1, her father is 4, her grandfather is 7, and the total * * * is 12, and 108 corresponds to 65438.