121. 3X
– 5y = 5 ….(I) and x/ y =5/7
7X= 5X = 5y 2X = 5y =0 .. (II)
Subtracting (II) from (I), we get: X =5.
Putting X =5 in (I), we get: y =2. So, x –y = 5 -2 =3.
122. 4
X + 3y = 18xy …(I) and 2 x -5y= - 4xy
Dividing (I) and (II) by X y, we get: 3/X + 4/y = 18…..(III) and 5/X –
2/y = 4…(iv)
Multiplying (iv) by 2 and adding (III) to it, we get: 13/x = 26 or x = 1/2.
Putting X = ½ in (III), we get: y = 1/3.
123. 2X
+ y =17 …(I); Y + 2z =15 …(II) and x + y =9
Subtracting (III) from (I), we
get: X =8.
Putting X =8 in (I), we get: y =
1. Putting =1 in (II-, we get: 2z =14 or z=7.
4
X + 3y X z = 4 x 8 + 3 x 1 + 7 = 42.
124. 3
X – 4y + z =7 .. (I) ; 2 X + 3y – z
= 19…. (II) and x + 2y +2z = 24….. (III)
Adding (I), (II), we get: 5x –y =26
Subtracting (I) from (II) and adding to (III), we get: 9y =36 or y =4.
Putting y =4 in (iv), we get: 5X – y =26.
