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While reading the problem, I re-wrote in the following way: 36/10000 * 28/10 * 100 / 4 * 10/1 * 1000/3 Simplifying further, Answer = A = 840
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With these kinds of equations the best thing to do is move the decimal places to the right, remember, what you move in the numerator has to occur in the denominator.

1) ORIGINAL EQUATION: (0.0036)(2.8) / (0.04)(0.1)(0.003)

2) MOVE 2.8 TWO PLACES TO THE RIGHT AND MOVE 0.04 TWO PLACES TO THE RIGHT, EQUATION THEN BECOMES: (0.0036)(280) / (4)(0.1)(0.003) YOU CAN NOW DIVIDE 280 BY 4 - CANCEL OUT THE FOUR AND THE 280 BECOMES 70

3) MOVE 0.0036 ONE PLACE TO THE RIGHT AND MOVE 0.1 IN THE DENOMINATOR ONE PLACE TO THE RIGHT, EQUATION THEN BECOMES: (0.036) (70) / (1) (0.003)

4) AGAIN MOVE 0.036 TWO PLACES TO THE RIGHT AND MOVE 0.003 TWO PLACES TO THE RIGHT, EQUATION THEN BECOMES: (36)(70) / (1)(3)

5) CANCEL OUT THE THREE AND THE 36 TO FURTHER SIMPLIFY, YOUR EQUATION THEN BECOMES 12*70 = 840 WHICH IS ANSWET CHOICE A

With questions like this, take a look at the answers first. Notice the only distinction between the answers is the factor of ten; thus, an exact calculation is not necessary to solve the problem, just a quick approximation.

.0036*2.8 is ~.0036*3, which can be approximated to .01.

.04*.1 = .004

Thus we have (.01)/(.004*.003). We can cancel out the powers of ten to give us 1/(.4*.003), which is 1/(.0012).

.0012 in fraction form is 12/10,000. Thus, our answer is can be given as 10,000/12.

840 is the only answer that comes close. Answer:A

Using the approximation method you can easily solve this question in 1:30 - 2:00.

I found my approach to be the quickest available and I'd like to share it with you guys:

(0.0036 x 2.8)/(0.04x0.1x0.003) -> expand numerator and denominator by 10^6 (since there are 5 decimal places in the numerator and 6 decimal places in the denominator) this yields: (360x28)/(4x1x3) -> cancel (120x7)/(1x1x1)= 120x7 = 840 -> A

Given that (0.0036)(2.8) / (0.04)(0.1)(0.003) = [(36/1000)(28/10)] / [(4/100)(1/10)(3/100)] = [(36*28)/(10000)] / [(4*1*3)/(100*10*100)] = [(36*28)/(4*1*3)] * [(100*10*100) / 10000] = (3*28) * 10 = 840 Hence option A

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Given that (0.0036)(2.8) / (0.04)(0.1)(0.003) = [(36/1000)(28/10)] / [(4/100)(1/10)(3/100)] = [(36*28)/(10000)] / [(4*1*3)/(100*10*100)] = [(36*28)/(4*1*3)] * [(100*10*100) / 10000] = (3*28) * 10 = 840 Hence option A

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Not sure if this is the right way to approach the answer, since the answer choices have big separation, I decided to approximate. (0.0036)(2.8) / (0.04)(0.1)(0.003) = (4∗10^−3)∗(3)/[(4∗10^−2)(1∗10^−1)∗(3∗10^−3)] = 1*10^3 = ~1000 Closest Ans to 1000 is C: 840
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If you analyze enough data, you can predict the future.....its calculating probability, nothing more!

No need to calculate for non-zero terms as it has to be 84.. check the decimal points.. Numerator has 5 and denominator has 6, so answer should be 6-5 =1 digit before decimal point or 8.4
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