Q37 Math - Equations

Hagrid · #1 (**permalink**) June 17th, 2009, 07:05 AM

Difficulty Level : Medium
Time to Solve : <60 secs

Please discuss your approach and also provide time you took to solve the question.

Q. What is the value of x?
A) 4x+9y = 10
B) 13x+29.25y = 32.5

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marcus fenix · #2 (**permalink**) June 17th, 2009, 11:05 AM

Neither A nor B is sufficient, as both are the same equation. Multiply A by 13 or B by 4, both give the same equation 52x + 117y = 130.

Time taken 90 secs (mainly due to multiplication

).

So answer is E.

yogami · #3 (**permalink**) June 18th, 2009, 12:22 AM

13/4 = 29.25/9 so E) 10 seconds

clerk · #4 (**permalink**) June 18th, 2009, 12:24 AM

20 sec,
E
Easily seen that numbers are the same, but just multiplied. In order to be sure, quickly find multiplier - better to do this by dividing 32.5 by 10 - 3,25
then multiple 4 and 3,25 - 13
9*3,25 - 29,25

docaseem · #5 (**permalink**) June 18th, 2009, 02:45 AM

Answer is E
Multiplying equation I wid 3.25 gives equation II
30sec around

pssohal · #6 (**permalink**) June 18th, 2009, 05:30 AM

e

rkandell · #7 (**permalink**) June 18th, 2009, 08:49 AM

E - 45 secs

My explanation would look similar to the previous postings, so I won't bore anyone with details.

bdsikma · #8 (**permalink**) June 18th, 2009, 02:08 PM

E-1 minute.

I immediately thought "C" because 2 unknowns require the same number of linear equations to solve, and choices 1 and 2 appear to be two linear equations. But as mentioned above, they are one and the same. A good trick on a medium level difficulty problem. I didn't immediately see the relationship though unlike some of you human calculators, so I tested them with a quick matrix of coefficients rather than screw around with division or trying to find the correct multiplier. It also makes it simpler by discarding the need to check the right side of the equations.

Take the coefficients and arrange them like so:

4___9
13__29.25

Then multiply from bottom left to top right, and again from bottom right to top left. Those numbers are both the same: 117. On a "gift" question like this, you don't have time to waste messing around.