Question

Stiind ca a + d = 17 si b + c = 19 , atunci numarul n = a * b + a * c + b * d + c * d este egal cu ....................................... .

Answer 1

a+d=17
b+c=19
a*b+a*c+b*d+c*d= a(b+c)+d(b+c)=(b+c)(a+d)=17*19=323

Answer 2

$a+d=17~;~b+c=19 \\ n=a \cdot b+a \cdot c +b \cdot d +c \cdot d \\ n=ab+ac+bd+cd \\ n=a(b+c)+d(b+c) \\ n=(b+c)(a+d) \\ n=19 \cdot 17 \\ \boxed {n=323}$