if the average ( arithmetic mean ) of a and b is 210 , and the average of b and c is 160 , what is the value of a − c ?
"question : a - c = ? ( a + b ) / 2 = 210 = = = > a + b = 420 ( b + c ) / 2 = 160 = = = > b + c = 320 ( a + b ) - ( b + c ) = 420 - 320 = = = > a + b - b - c = 100 = = = > a - c = 100 answer : c"
subtract(multiply(const_60.0, const_2), multiply(210, const_2))