Maths 急 列式

Let $ x be the elder sister received , $ y be the younger sister received :
x + y = 120 ...... (1)
{
x/5 - y/6 = 13 ...... (2)By (1) , y = 120 - x , sub. into (2) :
x/5 - (120 - x)/6 = 13
6x - 5(120 - x) = 13 * 30
6x - 600 + 5x = 390
11x = 990
x = 90
y = 120 - 90 = 30
The elder sister received $90 , the younger sister received $30.

Let $ x be the elder sister received , $ y be the younger sister received:

x+y=120..............(1)
x/5-y/6=13...........(2)
by(1) Move x or y
x=120-y or y=120-x
(1)Substituting(2)
(120-y)/5-y/6=13
6(120-y)-y*5=13*30
720-6y-5y=390
-11y=390-720
-11y=-330
-y=-30
y=30....(3)
(3)Substituting(1)
x+(30)=120
x=90
if you are not Substituting the x=120-y you can Substituting the y=120-x
y=120-x:
(1)Substituting(2)
x/5-(120-x)/6=13
6x-5(120-x)=13 * 30
6x-600+5x=390
11x=990
x=90...(3)
(3)Substituting(1)
90+y=120
y=120-90
y=30

Let x be the elder sister received,
let y be the younger sister received.
x+y=120.................(1)
x/5-y/6=13..............(2)
(2)x30 6x-5y=390.....(3)
x=120-y
sub.(3)
6(120-y)-5y=390
720-6y-5y=390
720-11y=390
y=30
x=90