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fractions

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by beater » Thu Sep 04, 2008 9:41 am
Which of the following fractions has the greatest value?



(a). 6 / 2^2 *5 ^2
(b). 1 / 2 ^ 3 * 5 ^ 2
(c). 28 / 2 ^ 2 * 5 ^ 3
(d). 62 / 2 ^ 3 * 5 ^ 3
(e). 122 / 2 ^ 4 * 5 ^ 3

Could one of you please outline a time effective method to solve this problem. Thanks
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Source: — Problem Solving |

by smithpa2 » Thu Sep 04, 2008 10:09 am
One method you couold try is to factor our common terms. For instance, you could factor out (1/(2^2*5^2) from value.

A) 6
B) 1/2
C) 28/5
D) 62/(2*5)
E) 122/(2^2*5)
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by mals24 » Thu Sep 04, 2008 10:58 am
IMO D

Ok firstly dont freak out looking at such questions there is always a simple way to solve these questions.

In this question if you notice the denominator in each fraction has a similar pattern. Its the product of 2 raised to some value with 5 raised to some value.

Try to make the denominators equal in each case by finding the GCD for the fractions in order to make comparisons simple.

The GCD in this case is 2^4*5^3

Convert the denominator of each fraction in 2^4*5^3 form

(a). 6 / 2^2 *5 ^2

6*2^2*5/ 2^4*5^3

(b). 1 / 2 ^ 3 * 5 ^ 2

1*2*5/2^4*5^3

(c). 28 / 2 ^ 2 * 5 ^ 3

28*2^2/2^4*5^3

(d). 62 / 2 ^ 3 * 5 ^ 3

62*2/2^4*5^3

(e). 122 / 2 ^ 4 * 5 ^ 3

Now since the denominators are same just compare the numerators and select the fraction which has the highest numerator.

Numerators of each fraction will be

a) 6*4*5 = 120
b) 2*5 = 10
c) 28*2 = 56
d) 62*10 = 620
e) 122

Hence the ans is D
Ok this process looks very time consuming but it isnt once you understand the logic behind it. It barely took more than a minute to solve it this way.
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