Question

[phuong the]

Tìm số ngyên x, biết : x/6+x/10+x/15+x/21+x/28+x/36+x/45+x/55+x/66+x/78=220/39

Answer 1

[Nguyễn Đình Toàn]

(x/6+x/10+...+x/66+x/78)*2=220/39*2

x/12+x/20+...x/132+x/156=440/39

x/2-x/3+x/3-x/4+...+x/11-x/12+x/12-x/13=440/39

x/2-x/13=440/39

11x/26=440/39

33x/78=880/78

33x=880

x=880/33

x=80/3=26, (6)