Question

Si $\frac{a}{3} = \frac{b}{7} = \frac{c}{4}$ ; a+b+c= 84
Hallar: b+c

Answer 1

a/3 = b/7:

7a = 3b:   b = 7a/3

a/3 = c/4:  c = 4a/3

a + b + c = 84

Reemplazo b y c por sus valores de a

a + (7a/3) + (4a/3) = 84

3a/3 + 7a/3  + 4a/3 = 84

(3a + 7a + 4a)/3 = 84

14a/3 = 84

14a = 3(84)

14a = 252

a = 18

Ahora hallo b y c

b = 7a/3

b = 7(18)/3 = 42

c = 4a/3  = 4(18)/3

c = 24

a = 18; b = 42; c = 24

b + c = 42 + 24 = 66

b + c = 66