Given lo g 1 0 1 2 , b = lo g 1 0 6 , c = lo g 1 0 2
What is the value of 9 a − b − c ?
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The given values can be rewritten as
1 0 a = 1 2 1 0 b = 6 1 0 c = 2 ⇒ 1 0 2 c = 2
As we know 6 × 2 = 1 2
∴ 1 0 b × 1 0 2 c = 1 0 a
1 0 b + 2 c = 1 0 a
∴ b + 2 c = a ⇒ a − b = 2 c
we have to find 9 a − b − c ⇒ 9 2 c − c ⇒ 9 c
9 lo g 2 2 1 ⇒ 3 lo g 2 ⇒ 1 . 3 9
Hence our answer is 1 . 3 9
I believe that the problem creator wanted to ask for 9 a − b − 2 c instead.
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I too think that
No...this question was in my School Maths book..I just wanted to share this question :D
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What is the name of that book
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@Meet Patel – S.Chand's ICSE Mathematics for class IX
a = lo g 1 0 1 2 , b = lo g 1 0 6 , c = lo g 1 0 2 a − b − c = lo g 1 0 1 2 − lo g 1 0 6 − lo g 1 0 2 = lo g 1 0 2 9 lo g 1 0 2 = 3 lo g 1 0 2 ≈ 1 . 3 9
Simple standard approach.
With these options, it's easy to find the right one without manipulation. a is a little over one, b somewhat under one, and c can't be much at all. 1.39 is the only answer remotely between 9^0 and 9^1.
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a − b − c = lo g 1 0 1 2 − lo g 1 0 6 − lo g 1 0 2 = lo g 1 0 2 − 2 lo g 1 0 2 = lo g 1 0 2 1 0 lo g 1 0 2 = 2 = 1 . 4 4 0 < 9 lo g 1 0 2 < 1 0 lo g 1 0 2 T h e o n l y o p t i o n t h a t s a t i s f i e s t h a t i s A : 1 . 3 9