If `2a + 3b + 4c = 35 and 3a + 5b + 7c = 30`, then `a + b + c =` _____

If a : b = 3 : 5 and b : c = 4 : 7 , find a : b : c

If a: b= 2: 3, b: c= 4: 5 and c: d= 6: 7 , find : a: b: c:d .

If a, b, c, d satisfy the equation a + 7b + 3c + 5d = 0 , 8a + 4b + 6c + 2d = - 16 , 2a + 6b + 4c + 8d =16 and 5a + 3b + 7c + d = -16 then the value of (a + d) (b + c) =______

If A = { 3 , 5 , 7 , 9 , 4 }, B = { 1, 3, 5 } , C = { 2, 4, 6 ,7 } ; then A - { B ∩ C } =

Add : 3b - 7c + 10, 5c - 2b - 15, 15 + 12c + b