If a varies directly as b, and a = 28 when b = 7, find b when a = 5. a 4/5 b 5/4 c 39.2

Option B.

Step-by-step explanation:

If a varies directly with b then when a increases b it also increases by a factor k.

Then we can write that

We know that when a = 28 then b = 7. So

Therefore the equation of proportionality is:

So when  then:

ANSWER

The correct choice is B.

EXPLANATION

If 'a' varies directly as 'b' then we write the equation of variation,

Where k is the constant of variation.

We have that a = 28 when b = 7.

This implies that,

The equation now becomes

When we a=5, we have

The correct answer is B

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step-by-step explanation: