Question

15.
If 3x + 5y = 10 and 3y+5x = 30 then aver-
age if'x' and 'y' is?
A 3/2
B. 4
C. 5/2
D. 7/2​

Answer 1

Answer:

Solving by elimination method

3x + 5y = 10 ................eq (1)

5x + 3y = 30 ...............eq (2)

Multiply eq (1) by 5 and eq (2) by 3

We get

15x + 25y - 50 = 0..............eq (3)

15x + 9y - 90 = 0..............eq (4)

Subtract eq (4) from eq (3)

eq (3) - eq (4)

(15x + 25y - 50) - (15x + 9y - 90) = 0

25y - 9y - 50 + 90 = 0

16y + 40 = 0

y = 40/16

y = 5/2

Putting y = 5/2 in eq (1)

3x + 5 x (5/2) = 10

$3x + \frac{25}{2} = 10$

$3x = 10 - \frac{25}{2}$

$3x = \frac{20 - 25}{2}$

3x = -5/2

x = -5/6

y = 5/2

Average =

$\frac{x + y}{2}$

$( \frac{5}{2} + \frac{ - 5}{6} ) \div 2$

$\frac{ 15 - 5}{6} \div 2$

$\frac{10}{6} \div 2$

$\frac{10}{6} \times \frac{1}{2}$

5/6 Answer.