Some young pioneers planted 20 trees along both sides of a street. They planted trees every 4 meters including the ends of the street. How long is the street?

meters

There is the same number of trees on each side, so we can just look at one side to find the total length of the street. There are 20 ÷ 2 = 10trees on each side of the street, so there are 10 - 1 = 9 non-zero multiples of 4 on the street. This means that the street is (10 – 1) × 4 = 36 meters long.