a DS question but what if we were to solve

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shoot4greatness: Master | Next Rank: 500 Posts; Posts: 100; Joined: Sat Sep 11, 2010 6:57 pm; Thanked: 2 times

by shoot4greatness » Tue May 31, 2011 12:34 pm

the inflation index for the year 1989 relative to the year 1970 was 3.56, indicating that, on the average, for each dollar spend in 1970 for goods, $3.56 had to be spent for the same goods in 1989. If the price of Model K mixer increased precisely according to the inflation index, what was the price of the mixer in 1970?

1. the price of the Model K mixer was $102.40 more in 1989 than in 1970

2. the price of the model K mixer was $142.40 in 1989

The answer is d

if we were to solve, for instance 1, do we divide the 102.40 by the inflation index to solve for the price in 70 or do we just leave the increase as is?

Last edited by shoot4greatness on Tue May 31, 2011 2:59 pm, edited 1 time in total.

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Source: Beat The GMAT — Problem Solving | Tue May 31, 2011 12:34 pm

bajwa2307: Senior | Next Rank: 100 Posts; Posts: 40; Joined: Tue Jan 18, 2011 5:14 amFollowed by: 2 members; Location: Bangalore; Thanked: 3 times

by bajwa2307 » Tue May 31, 2011 12:53 pm

are you sure that the answer is c?

let price in 1970 be x
let price in 1989 be y

so by statement 1, we have

y - x = 102.40

now we know that 3.56x = y

so substitute the value of y in equation and solve for X, hence 1 is sufficient

by using statement 2, we have

y = 142.40

use the relation, 3.56x = y

substitute the value of y and solve for x, so 2 alone is also sufficient

I think the answer should be D or am I doing something wrong here?

Verbal is testing my patience

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SoCan: Senior | Next Rank: 100 Posts; Posts: 97; Joined: Sun May 15, 2011 9:19 amFollowed by: 1 member; Thanked: 18 times

by SoCan » Tue May 31, 2011 1:33 pm

Answer is definitely D, not C

x=price in 1970

1) x=(x+102.4)/3.56
3.56x=x+102.4
2.56x=102.4
x=40

2) x=142.40/3.56
x=40

What source gave you C?

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shoot4greatness: Master | Next Rank: 500 Posts; Posts: 100; Joined: Sat Sep 11, 2010 6:57 pm; Thanked: 2 times

by shoot4greatness » Tue May 31, 2011 2:57 pm

Sorry typo yes its d

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serendipiteez: Junior | Next Rank: 30 Posts; Posts: 25; Joined: Wed Feb 13, 2013 9:25 pm; Thanked: 2 times

by serendipiteez » Sun May 26, 2013 4:40 am

My gut feel was "How does knowing what it increased by tell me anything about the original price?" and then I moved on. But clearly, there's an algebraic solution.

Generally speaking, if we know the difference in prices between two dates like this example, can we always solve and get an answer?

I'm trying to understand whether this is just a special case where it just worked out or can this be taken as a general rule?

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