Question

If 3a + 4b = 4a - 4b = 21, find the value of a.
(a) 3
(b) 6
(c) 21
(d) 42
(e) the answer cannot be determined from the information given.

Answer 1

two equal signs? is this written right?

Answer 2

yup

Answer 3

well i assume it means 3a + 4b = 4a - 4b

subtract 3a from both sides

4b = a - 4b

add 4b to both sides

8b = a = 21

so this is equal to 21?

a = 21

8b = 21
b = 21/8

does that make sense? o.O

Answer 4

i think you're supposed to add the 2 equations. then you get a is 6 and then b is 3/4

Answer 5

a=6

Answer 6

yeah thanks

Answer 7

and b=3/4

Answer 8

like i said this question doesnt make sense -_-

Answer 9

so you did

3a + 4b = 21
4a - 4b = 21

7a = 42
a = 6
??

Answer 10

yes

Answer 11

yeah that makes more sense...

Answer 12

if u have doubts see here
http://www.wolframalpha.com/input/?i=+3a+%2B+4b+%3D+4a+-+4b+%3D+21+find+a

Answer 13

but seriously...two equal signs dont make sense :|

Answer 14

it don't it would seem like the answer is E

Answer 15

i mean (b) oops

Answer 16

well if the question meant what you did...then 6 is right

Answer 17

and also if you check

3(6) + 4(3/4) = 21
18 + 3 = 21
21 = 21

4(6) - 4(3/4) = 21
24 - 3 = 21
21 = 21

Answer 18

so yeah. 6 would be right

Answer 19

but still poor sense of notation =_=

Answer 20

idk it was an sat question