The working efficiency of Party A and Party B in one day is 1 ÷ 6 = 1/6, Party A can complete 8/ 15 of this project in two days, and Party B can complete it in five days, which can be regarded as two days of cooperation, and (5-2) = 3 days of working alone, so the working efficiency of Party B in one day is:

[8/ 15-( 1/6)×2]÷(5-2)= 1/ 15

Then the working efficiency of a day is1/6-115 =110.

Therefore, if Party A does this project alone, it will take1÷110 =10 days to complete it.

Solution: Because 4/5 of the coal in Pile A was transported away and 75% of the coal in Pile A was transported away, the remaining coal was exactly equal, that is to say,

(1-4/5) Coal pile A = (1-75%) Coal pile B = 1/5 Coal pile A = 1/4 Coal pile B.

So the ratio of two piles of coal is 5: 4, so the result is

Coal in Pile A: 72× [5 ÷ (5+4)] = 40 tons.

B has 72-40 = 32 tons of coal or 72× [4 ÷ (5+4)] = 32 tons.

Solution: continuous odd numbers mean that the latter number is 2 larger than the previous number. These three continuous odd numbers can be set to X, X+2 and X+4.

Then when the smallest odd number x is expanded to 3 times of it, that is, 3X, the sum of the three numbers is 3x+x+2+x+4 = 10 1.

Then the smallest odd number is (101-2-4) ÷ (1+1+3) =19.

Solution: Decomposition prime factor 364 = 2× 2× 7×13 = 4× 91= 28×13 = 7× 52.

So when there are 9 1- 1 = 90 students, each person will have 4 trees;

When there are 28- 1 = 27 students, each race has 13 trees;

When there are 52- 1 = 5 1 students, each race has 7 trees;