the sum of three numbers a, b, and c is 240. if sum of a and b is 160 , sum of a and c is 170 then b+c-a equal to

Diketahui :
a + b + c = 240
a + b = 160
a + c = 170

Ditanya :
b + c - a = ??

Dijawab :

   a + b = 160
160 + c = 240
          c = 240 - 160
          c = 80

  a + c = 170
a + 80 = 170
        a = 170 - 80
        a = 90

a + b = 160
90 + b = 160
        b = 160 - 90
        b = 70

Jadi b + c - a = 70 + 80 - 90 = 60