Numeric Prob
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Source: Beat The GMAT — Problem Solving |
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sudhir3127
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are you sure the question reads X = (√3 + √5)222 and not
X = (√3 + √5)^222...
X = (√3 + √5)^222...
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parallel_chase
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if the question is (√3 + √5)222 then 8 will be after the decimal point.
√3 ~ 1.7
√5 ~ 2.2
(1.7+2.2)222 = 3.9*222 = 765.8
now if the question is (√3 + √5)^222 then you would probably have to use modular arithmetic.
√3 ~ 1.7
√5 ~ 2.2
(1.7+2.2)222 = 3.9*222 = 765.8
now if the question is (√3 + √5)^222 then you would probably have to use modular arithmetic.
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pepeprepa
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Chase I did approximations and I was wrong because the digit is 9.
I did with 1 like you.
(1,7 + 2,2)*222=865.8
I did with 2 after looking at the values of these sqrt
(1,73+2,23)*222=879.12
I finally checked with excel and with the real values of sqrt 3 and 5, the result is:
880.922
I wonder if it is possible to answer this question.
I did with 1 like you.
(1,7 + 2,2)*222=865.8
I did with 2 after looking at the values of these sqrt
(1,73+2,23)*222=879.12
I finally checked with excel and with the real values of sqrt 3 and 5, the result is:
880.922
I wonder if it is possible to answer this question.
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sudhir3127
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i know for sure the answer is 6.
heres what i did..
(√3 + √5)^222
= ((sq rt 3 + sq rt 5 )^2)^111
= ( 8 +2sqrt 15)^111
we know for sure that (2sqrt 15)^111 will only give us the decimal.
(2sqrt 15)^111 will be (2sqrt 15) ( (2sqrt 15)^111
root 15 if we take only 2 decimal point is 3.8
hence 2*3.8 = 7.6
hence the answer is 6.
but then if we take more decimals our answer changes.. so i am ot very sure abt the technique...
PS: i used scientific calculator to find the answer and its indeed 6 as the answer.
heres what i did..
(√3 + √5)^222
= ((sq rt 3 + sq rt 5 )^2)^111
= ( 8 +2sqrt 15)^111
we know for sure that (2sqrt 15)^111 will only give us the decimal.
(2sqrt 15)^111 will be (2sqrt 15) ( (2sqrt 15)^111
root 15 if we take only 2 decimal point is 3.8
hence 2*3.8 = 7.6
hence the answer is 6.
but then if we take more decimals our answer changes.. so i am ot very sure abt the technique...
PS: i used scientific calculator to find the answer and its indeed 6 as the answer.
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parallel_chase
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You are absolutely right if we take more decimals the answer will change to 7.
Your method is correct, but which question is correct your question or KARTIK's question, secondly the question does not mention limit for the decimal range.
What is the OA?
Your method is correct, but which question is correct your question or KARTIK's question, secondly the question does not mention limit for the decimal range.
What is the OA?
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parallel_chase
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Here is the real question and of course the answer is 6.
(√3 + √5)^222 = ((√3 + √5)^2)^111 = (3+5+2√3.√5)^111
or (8+2√3.√5)^111.
(2√3.√5)^111.
Now 111th power of √3 and √5 will leave √3 and √5 at the end .
So then just multiply 2.√3.√5 and the first decimal is 6.
This question is not from GMAT, Therefore, even if you cant get it right nothing to worry.
(√3 + √5)^222 = ((√3 + √5)^2)^111 = (3+5+2√3.√5)^111
or (8+2√3.√5)^111.
(2√3.√5)^111.
Now 111th power of √3 and √5 will leave √3 and √5 at the end .
So then just multiply 2.√3.√5 and the first decimal is 6.
This question is not from GMAT, Therefore, even if you cant get it right nothing to worry.
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sudhir3127
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good stuff chase...
as i said .. when we multiply 2.√3.√5 and the first decimal is 6
we need to be careful abt the decimal places. as the above multiplication doesnt actually give u 6 ( its gives 7) if we take more one decimal place..
as i said .. when we multiply 2.√3.√5 and the first decimal is 6
we need to be careful abt the decimal places. as the above multiplication doesnt actually give u 6 ( its gives 7) if we take more one decimal place..
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pepeprepa
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I don't follow how you know that
if 2.√3.√5 has a first decimal of 6
then (2.√3.√5)*(2.√3.√5)^110 has a first decimal of 6
then (8+2√3.√5)^111 has a first decimal of 6 ?
What I think is that these numbers also multiply the decimals...
Just to be sure, "the first digit after the decimal point", it talks about the tenths right?
if 2.√3.√5 has a first decimal of 6
then (2.√3.√5)*(2.√3.√5)^110 has a first decimal of 6
then (8+2√3.√5)^111 has a first decimal of 6 ?
What I think is that these numbers also multiply the decimals...
Just to be sure, "the first digit after the decimal point", it talks about the tenths right?
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Rosen_Kralev
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Hi everyone,
(√5 + √3)^222 + (√5 - √3)^222
is an integer.
√5 - √3 is pretty small (less than 0.9, for all we care) and so you can bet that when raised to the 222nd power, it will be tiny (to be read: less than 0.1)
Have fun! I just found out about this message board by chance and don't have to go through all problems, but if there's something anyone is stuck on, please email me and I'd be more than happy to help.
(√5 + √3)^222 + (√5 - √3)^222
is an integer.
√5 - √3 is pretty small (less than 0.9, for all we care) and so you can bet that when raised to the 222nd power, it will be tiny (to be read: less than 0.1)
Have fun! I just found out about this message board by chance and don't have to go through all problems, but if there's something anyone is stuck on, please email me and I'd be more than happy to help.
