Let →a,→b and →c be three non-zero and non-coplanar vectors and →p,→q and →r be three vectors given by →p=→a+→b−2→c, →q=3→a−2→b+→c and →r=→a−4→b+2→c. If the volume of the parallelopiped determined by →a,→b and →c is V1 and the volume of the parallelopiped determined by →p,→q and →r is V2 then V2:V1=