5M？ + 12M？ +23M？ =(50×40)x

200x =40M？

x = 40÷ 200

= 0.2 m

Answer: It can be 0.2M thick.

Analysis: Cement, stone and sand are a volume. Paving such a large volume of road. The surface area of the playground is 50*40. Divide the total volume by the surface area to get the height. Namely the thickness of the road. (Volume = length * width * height)

Question 2: Setting: After X days, the rice will be finished.

2*( 15X)=20X+80

30X=20X+80

10X=80

X=8 days

Weight of rice: 15 * 8 = 120kg.

Weight of flour: 2 * 120-240kg.

A: Yes. . . .

Analysis: Eat 15 kg of rice every day for ***x days. So the total weight of rice is 15*x kg. Eat 20 kilograms of flour every day for ***x days, and there are 80 kilograms left. So the total amount of flour is 20*x+80 kg. And because the weight of flour is twice that of rice. So the equation is listed: 2*( 15X)=20X+80.

This is the step and process to solve the problem. Hope to adopt ~ ~ ~