(2+5)÷2=3.5
(2+5+5)÷3=4
(2+5*n)÷(1+n)=4.9
2+5n=4.9(n+1)
5n-4.9n=4.9-2
0.1n=4.7
n=475n-4.9n=4.9-20.1n=2.9n=29不好意思写错了(2+5)÷2=3.5 (2+5+5)÷3=4 (2+5*n)÷(1+n)=4.9 2+5n=4.9(n+1)5n-4.9n=4.9-20.1n=2.9n=29