m 2 = 2 3 × 3 4 × 5 6
If m is positive, which of the following statements is true?
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Nice way of using 7 < 5 0 < 8 , so that you don't need to know what 2 is.
Um can someone please explain this to me? I thought all we needed to do was this 2^3=8 3^4=81 5^6=15625 15625+81+8=15714 and then square root 15714 to get your answer. this way its 15625+81+8=M^2 and then square root it and you get M=125.3
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If you had a calculator, then yes that is a possible approach. The idea that I was going for, was how to solve this problem without external calculation aids.
You're going along the right lines but you're meant to be multiplying all of those powers, not adding them, which might make this a little time-consuming without a calculator.
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I actually did evaluate the whole right side in my head without calculator or paper. It took me 3 minutes though. I got 10 125 000 which is between $3000^2$ and $4000^2$ . Btw it is good excersise for your brain to do hard calculations in your head. It takes time to learn all the tricks but it's worth it.
Well um, i don't understand how do u group it..
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Simply multiply some of the terms together: (10 * 9 * 5)^2 => (2 5 * 3 3 * 5)^2 ; (10 * 5) => (2*5 * 5) ; Thus, this "grouping" of the terms really simplifies it more than how it is originally laid out. [(10 * 9 * 5)^2] * (10 * 5) is really the same thing as (2^3) * (3^4) * (5^6).
m 2 = 2 3 × 3 4 × 5 6
m = 8 × 3 2 × 5 3
m = 2 × 2 × 9 × 1 2 5
m = 2 2 5 0 × 2
m = 2 2 5 0 × ( 1 . 4 1 4 )
m = 3 1 8 1 . 5
S o , 3 0 0 0 < m < 4 0 0 0 : )
i did this in sme way
You are supposed to "Estimate" and not "Find out " the value of "M"
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In this problem, the computational complexity of finding the exact solution is the same as estimating it.
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I disagree. It is much easier to estimate then it is to find the exact value. There are several solutions (and comments) which illustrate as such.
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@Chung Kevin – In the brilliance of Nihar Mahajan estimating is waste of time when solving can be made easy.
Not at all. Look at this- The above expression equals - 4 0 ∗ 8 1 ∗ 3 1 2 5 = 3 2 0 0 ∗ 3 1 2 5 ...thus its just a matter of few seconds to get it from here.
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@Krishna Ar – Getting to the result in this manner required that you either 'knew' that 5 5 = 3 1 2 5 or had to do the computation.
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@Janardhanan Sivaramakrishnan – U need not know 5^5 Or 5^6 I just divided power by 2 and everyone know what 5^3 is. So calculations are better way and because the range is huge so i used 2^(1/2) as 1.5 Instead of 1.414 or whatever
@Krishna Ar – It was actually simple ......but the problem is while answering it on my smartphone ......it sensed a touch while scrolling
m = 3181.5 is not the actual value of 'm' . It is estimated , because 2^(1/2) is not actually equal to 1.414 .
could someone explain why doing m = 2^3/2 * 3^2 * 5^3 is not correct? I thought that sqrt(2^3) = 2^3/2 nevermind it turns out google though 2^3/2 was 2^3 / 2 doh!
Or -3181.5....
2 2 × 3 4 × 5 6 < m 2 < 2 4 × 3 4 × 5 6 ⇒ 2 × 3 2 × 5 3 < m < 2 2 × 3 2 × 5 3 ⇒ 2 2 5 0 < m < 4 5 0 0 . Now m = 2 2 5 0 2 ∴ 3 0 0 0 < m < 4 0 0 0
I felt that people would know that 2 ≈ 1 . 4 , and thus that 1 . 4 < 2 < 1 . 5 , which would make 3 1 5 0 < m < 3 3 7 5 , and hence reach the answer. Of course, since I chose a wider range, there are many other ways to approximate it.
m 2 = 2 3 × 3 4 × 5 6 m 2 = 1 0 1 2 5 0 0 0 m = 1 0 1 2 5 0 0 0 m = 2 2 5 0 2 2 2 5 0 2 ≈ 3 1 8 2 ∴ 3 0 0 0 < m < 4 0 0 0
Taking the square root
m = 2 × 9 × 1 2 5 × 2 = ( 4 + 4 + 1 ) × 2 5 0 2 = 2 2 5 0 2
Now, as 1 < 2 < 1 . 5 ⇒ 2 0 0 0 < 2 2 5 0 < 2 2 5 0 2 = m < 3 3 7 5 < 4 0 0 0 .
The lower bound has to be slightly tighter, so that you know that m > 3 0 0 0 . Otherwise, you don't know if 2 0 0 0 < m < 3 0 0 0 which is one of the options.
m^2 = 2^3x 3^4x5^6 = 10125000. Root of 19125000 approximately more than 3000. So m lies between3000 & 4000.
Easy way is to find (4000) ^2 and (3000)^2 Therefore, we can surely say that m must be between 3000 and 4000 as other inequalities do not satisfy the equation
Sqrt (10125000) = 3181.9805 {Correct to 4 decimal places.}
Yes, that's valid too :)
I dont know about other languages but sqrt is a function in python . Do u know python ?? Or its just coincidence
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sqrt means square root. it's often used in many programming language
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Surely the poser does not expect us to evaluate the RHS directly!
By grouping the powers appropriately write
m 2 = ( 1 0 × 9 × 5 ) 2 ( 1 0 × 5 ) = 4 5 0 2 × 5 0
and so
m = 4 5 0 × 5 0
and so
4 5 0 × 4 9 < m < 4 5 0 × 6 4
and it follows that
4 5 0 × 7 < m < 4 5 0 × 8
⟹ 3 1 5 0 < m < 3 6 0 0
⟹ 3 0 0 0 < m < 4 0 0 0