Data Sufficiency

Does x+y=5?

1) 4x+y=17
2) x+4y=8

a) statement 1 alone sufficient
b) statement 2 alone sufficient
c) both
d) each statement alone
e) neither statement 1 and 2 together are sufficient

i picked d but it's actually c

can someone explain? thanks

Sprite_TM wrote:Does x+y=5?

1) 4x+y=17
2) x+4y=8

a) statement 1 alone sufficient
b) statement 2 alone sufficient
c) both
d) each statement alone
e) neither statement 1 and 2 together are sufficient

i picked d but it's actually c

can someone explain? thanks

Individually, we cannot find x+ y= 8

As you have incorrectly chosen D, take this example

x+y=8-3Y

so as depending on value of Y, X+Y will change so we dont have a specific value

when Y=1, x+y=5 ( Yes), when Y=2, x+y=!5 ( No) Insufficient

Add together

5x+5y=25

x+y=5
C

When you have two unknowns you can determine through two quad. equations. If you use the orig with any of the two individually you can find values for the individual variables. Not sure why statements alone are not Suffic.

Sprite_TM wrote:Does x+y=5?

1) 4x+y=17
2) x+4y=8

a) statement 1 alone sufficient
b) statement 2 alone sufficient
c) both
d) each statement alone
e) neither statement 1 and 2 together are sufficient

i picked d but it's actually c

can someone explain? thanks

1) 4x+y=17;
y=17-4x; when x=1; y=13; x+y=14 which is not equal to 5;
when x=4; y=1; x+y=5;
as we can see different results are possible for different values of x and y hence 1 alone is not sufficient to answer the question.

2) x+4y=8; similarly here consider y=1 and x=4 x+y=5;
for y=2; x=0; x+y=2; hence 2 alone is also not sufficient to answer the question.

combining 1 and 2 together,
we have;
x+4y=8;
4x+y=17;
upon solving above two equation we have x=4 and y=1; and x+y=5; as both equations are required to answer the question hence answer should be C

Here you can't use "x+y = 5?" and one of the other equations to solve because "x+y = 5?" is a question not a statement.

kalabok7 wrote:When you have two unknowns you can determine through two quad. equations. If you use the orig with any of the two individually you can find values for the individual variables. Not sure why statements alone are not Suffic.