1; y - 2/4 =1/2

2/9 +y = 1

y/4 =28

3: manh vuon hinh chu nhat co chieu rong bang 2/5 chieu dai va chieu dai hon chieu rong 24m tinh dien tich

4; tinh tong:

 1,2,3,4...,9

viet cach lam ra nhe