March 12 is the tree planting day. 170 students of grade three take part in the voluntary tree planting activities. If the average boy can dig three tree pits a day, and the average girl can plant seven trees a day, just to plant a tree in each tree pit, how many men and women are there in that grade?

March 12 is the tree planting day. 170 students of grade three take part in the voluntary tree planting activities. If the average boy can dig three tree pits a day, and the average girl can plant seven trees a day, just to plant a tree in each tree pit, how many men and women are there in that grade?

Suppose there are x boys and (170-x) girls in this grade. According to the meaning of the question, we can get: 3x = 7 (170-x), 3x = 1190-7x, 10x = 1190, & nbsp; X = 119170-x = 170-119 = 51. A: there are 119 boys and 51 girls in this grade

During the tree planting day, 100 teachers and students took part in tree planting. Each teacher planted 3 trees and two students planted one tree
How many students take part in tree planting?

If there are x teachers and y students, then:
①x+y=100
②3x+0.5y=100
X = 20, y = 80
There are 20 teachers and 80 students

On this year's tree planting day, students planted 180 trees, 20 of which did not survive. Later, we replanted 20 trees, all of which survived ．

According to the meaning of the question: 180 ÷ (180 + 20) = 90%