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Comment on Shortcut Involving Ratios and Fractions
Perhaps I did not calculate
-Yvonne
The cross simplification you
The cross simplification you're referring to is a technique we can use before MULTIPLYING two fractions.
For example, before multiplying 4/5 x 3/8, we might cross simplify to get 1/5 x 3/2, which makes our multiplication easier. For more on this technique, see https://www.gmatprepnow.com/module/gmat-arithmetic/video/1068 (starting at 4:00)
In your example, you are using the technique with EQUIVALENT FRACTIONS. To illustrate how this technique doesn't work, consider this example:
We know that 2/3 = 8/12
However, if we divide the 2 and 8 by 2, we get: 1/3 = 8/6, which is not a true statement.
i did this
6.25 = 6
6----90 multiplying factor 15
700----700*15=10,500
since we reduced denominator our value increased so option will be <10,500
hence d
is this approach correct??
I can see that the answer
I can see that the answer must be a little less than 10,500, however answer choice C also works. How do you know that the correct answer is D and not ?
Cheers,
Brent
hi Brent, I noticed that we
I'm not certain that the
I'm not certain that the unitary method is any faster for these kinds of questions. That said, regardless of which approach we use, we end up working with the same values any way.
Can you give me an example of a question in which the unitary method is faster?
what I have done:
6.25 = 6 -
so:
6-/90 = 700/x
2-/30 = 700 / x
x = 21000 / 2- = 10,500-. Answer D.
(I dont know if it is accurate... and fast...)
That approach isn't quite as
That approach isn't quite as accurate, because it should read: 6.25 = 6+ (since 6.25 is a little bit bigger than 6)
So, we end up with: x = 21,000/(2+) which means x is a little bit less than 10,500.
Answer choices D and E (9,920 and 10,080) are both a little bit less than 10,500
So, it's hard to tell which one is correct.
Hi Brent, another fast
6.25 g to do 90 CB; 700 G, how many CB?
700 is more or less 120 times more than 6.25 ( 100 --> 625. + 20 times).
90*120 --> 10080.
Cheers,
That approach works, but I
That approach works, but I would make one change:
Where you write "700 is more or less 120 times more than 6.25 ( 100 --> 625. + 20 times)", it should be "100 --> 625. + 11+ times."
700 - 625 = 75, and 6.25 divides into 75 a more than 11 times (12 times to be exact).
So, we get: (90)(111+) --> 9990+