Question

if 3x+7y=75 and x-3y=5 then the value of (x+y) is
options: a)80 b)40 c)20 d)17.5​

Answer 1

Answer:

x+y = 17.5(option d)

Step-by-step explanation:

3x+7y=75 = 1st equation..

x-3y=5 = 2nd equation.

multiply 2nd equation by 3, so we can cancel 3x and x..

AFTER MULTIPLY 2ND EQUATION BY 3 WE GET,

3x -9y = 15.

Now subtract 1st and 2nd equation.

3x+7y=75

(-) 3x -9y = 15

BEFORE SUBTRACTING CHANGE SIGN...

so now we get 16y = 50

y = 50/16

y = 25/8

Now, substitute y = 25/8 in any equation either 1 or 2

so, x-3(25/8) = 5

x = 115/8

Now as per the question x+y

we get 25÷8 + 115÷8

25+115 ÷ 8

140 ÷ 8

35 ÷ 2

SO, 17.5 IS THE ANSWER...( OPTION D)