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.
Putting x =6, y =4 in (III), we get: 2z = 10 or z =5.
125. 2x
= y = 15…(I); 2y + z = 25 ..(II) and 2 Z + x = 26.
Adding (I), (II) and (III), we
get: 3 (X + y + z) = 66 or x = Y + z = 22.
From (II), we have; y = 25 –z/ 2.
From (III), we have: x = 26 – 2z.
(26 – 2z) + ( 25 –z/2) + z
=22 77 – 3z = 33 z =11.
126. 2X
= 3y = 31 …(I) ; y – z =4
..(II) and x + 2z = 11
Multiplying (III) by 2 and
subtracting from (I), we get: 3y – 4z =9…(IV)
Solving (II) and (Iv), we get: y
=7, z =3. Putting y =7 in (I), we get: X =5.
X + y + z = (5 + 7 + 3)= 15.
127. Given
exp. = (3/4 x 4/3 x 5/3 x 3/5 /13/7 x 1/13) = 1/7.
128. Given
exp.= 1/2 x 2/3x ¾ x …..x (n -1) /n =
1/n.
129. Given
exp. 3/2 x 4/3 x 5/4 x////x 121 /120 = 121/2 = 60.5.
130. Given
exp. = 5/3 7/5 x 9/7 x …..x 1003 / 1001 = 1003 / 4.
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