20
he spent 70(60 + (80-70)) got 90

5 POINT STAR

Yes it is possible
a=b+c
b=d+e
c=f+g
d=h+i
e=j+k
f=l+m
g=n+o

Now suppose a is a middle number in 3 by 3 box
since any integer can be expressed as sum of two integers with infinite possibilities .following the above steps we  can understand a can be expressed as sum of h,I,j,k,l,m,n,o .with each variable having infinite possibiles.now at any point we can find infinite integers which can surround a satisfying given condition.this can be used for any number in the table.we will find 8 integers which we have not used .now expanding table we will never be restricted to choose one number for the numbers surrounding the boundaries of table there will at least be a option of choosing 2 now since we have used  limited numbers till now.there will be numbers having a required sum and uncommon with numbers we have used.so there will be no blockage in expanding our table

47 as there is still a case when we take 46 socks and 3 pairs are not there

Another answer and more precise one

(Any multiple of LCM of 2 to 10)-1

Example-

LCM of (2,3,4,5,6,7,8,9,10) = 2520
Solution–
(Any multiple of LCM of 2 to 10)-1
= 2520 – 1  = 2519

(Any multiple of 10!)-1

19

5

killing myself

ANY SPEED METRO ARE IN ROTATION