Interesting Mathematics in Autumn Edition of Grade Five in Primary School

1, length of express train: (18-10) ×10 = 80m; Length of local train: (18- 10) × 7 = 56m.

2. Let A and B be s meters apart, with speed A as V A and speed B as V B..

V a* S/(V A+V B)= 120； V B *3S/(V A +V B) -S= 150，

S=255 meters to solve this system of equations.

3. Xiaoming 100-30=70 points, and he owes 2 points from 70÷4= 18. It can be seen that he chose at least 18.

And 18× 4-2×1= 70-one possibility is to choose the right question18, and choose two wrong questions to get 70 points.

On this basis, if you choose the right question 1 again, you must choose four wrong questions to make the score even.

(30-18-2) ÷ (1+4) =10 ÷ 5 = 2, which means he can choose two more questions at most.

So Xiao Ming chose 18+2=20 questions at most.

4、(23+26+30+33)÷4=28。 The average of four is 28.