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a is directly proportional to b. If a = 8 when b = 2, what is a when b

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Bunuel
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a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink] New post   11 Jun 2018, 22:47
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a is directly proportional to b. If a = 8 when b = 2, what is a when b = 4?

(A) 10
(B) 16
(C) 32
(D) 64
(E) 128
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B
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Re: a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink] New post   11 Jun 2018, 22:52
Bunuel wrote:
a is directly proportional to b. If a = 8 when b = 2, what is a when b = 4?

(A) 10
(B) 16
(C) 32
(D) 64
(E) 128



ans: B

Once again a/b = A/B so
8/2=A/4 so A=16 ans.

Ans: B
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Re: a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink] New post   11 Jun 2018, 23:11
Bunuel wrote:
a is directly proportional to b. If a = 8 when b = 2, what is a when b = 4?

(A) 10
(B) 16
(C) 32
(D) 64
(E) 128


When a is directly proportional to b, we can say that a = kb where k is a constant.

We are told that if a = 8, b = 2. Now, 8 = k*2 -> Constant(k) = 4

Therefore, the value of a = kb = 4*4 = 16(Option B) when b = 4.
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Re: a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink] New post   12 Jun 2018, 00:17
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Solution



Given:
    • a is directly proportional to b
    • When b = 2, a = 8

To find:
    • The value of a, when b = 4

Approach and Working:
As a is directly proportional to b, a = k * b, where k is a constant

Given that, when b = 2, a = 8
    • Therefore, we can write 8 = k * 2
    Or, k = 4

    • Hence, a = 4b

When b = 4,
    • a = 4 * 4 = 16

Hence, the correct answer is option B.

Answer: B
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Re: a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink] New post   12 Jun 2018, 05:32
Bunuel wrote:
a is directly proportional to b. If a = 8 when b = 2, what is a when b = 4?

(A) 10
(B) 16
(C) 32
(D) 64
(E) 128



Note : a is directly proportional to b.

a is 8 when b is 2. It means a will be 4 times larger than b all time.

Now b is 4. what is a ?

4 times of b will be 16.

Thus the best answer is B.
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Re: a is directly proportional to b. If a = 8 when b = 2, what is a when b [#permalink]
12 Jun 2018, 05:32
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