The problem of circle, the formula and the answer The area of a square is 20 square centimeters. What is the area of the largest circle in the middle of the square? Please be sure to calculate the side length. The formula must be listed!

The problem of circle, the formula and the answer The area of a square is 20 square centimeters. What is the area of the largest circle in the middle of the square? Please be sure to calculate the side length. The formula must be listed!

20÷4×π
=5π
=15.7 (cm2)
20 / 4 is the square of the radius
The square of the radius x π is the area of the circle

Students go to the homes for the aged to take part in voluntary labor. Class five (1) goes to the homes for the aged every five days, and class five (2) goes to the homes for the aged every seven days. If class five (1) goes to the homes for the aged on March 16, and class five (2) goes to the homes for the aged on March 17?
There should be a formula. Quick, I'll add points if I answer it in 5 minutes. I won't offer a reward first. I'll give points to whoever answers first

（5-1）/（7-5）=2
So class two of five years went twice again on the same day as class one
17+7*2=31
So the two classes will go to the nursing home at the same time on March 31

2.3 hours later, the two cars meet. How many kilometers are there between a and B? (car: 55 km / h) (truck: 45 km / h) don't use the equation to solve it. We haven't learned the equation yet. I want to understand what you mean

Distance between a and B: (55 + 45) X2.3 = 230 (km)

1. A.bc * D.E = d.abc, which is a decimal multiplication formula expressed in letters. Each letter in the question represents a number

Question 1: because of D. ABC