Question

Please help me with these two problems :(

a + b = 11
a – b = 27


20c - 30d = 70
20c - 8d = -32

Answer 1

a + b = 11
a – b = 27
add the two equation to get
2a=38 --> a=19

b=11-a=11-19=-8

Answer 2

can you do the second one by yourself now?

Answer 3

WELL if I could have I would have done it myself.

Answer 4

I'll help walk you through it if you want. :)

Answer 5

20c - 30d = 70
20c - 8d = -32

First, I would multiply through by -1 to one of the equations.
So what would that give you ?

Answer 6

20c - 30d = 70 (eq1)
-1 * (20c - 8d) = -1*(-32) (eq2)

By multiplying eq2 by -1, then you are able to add the equations together and the C is eliminated.
( i suppose you could have just subtracted them, but adding is sometimes simpler)

-20c + 8d = 32 (eq2)

Answer 7

Can you take the new eq2 and add it to the original eq1 ?
Add these.
20c - 20c = 0

20c - 30d = 70 (eq1)
-20c + 8d = 32 (eq2)

What would that give you?