y varies directly as w². When y = 8, w = 2, find y when w = 3

y varies directly as w². When y = 8, w = 2, find y when w = 3

• A. 18
• B. 6
• C. 9
• D. 12

QUICK ANSWER…

A

SOLUTION…  

y α w²

y = Kw²

where k = constant.

Therefore,

y/w² = k = 8/2² = 8/4 = 2

Constant = 2, now let’s use the constant to solve for y when w = 3,

Again, y = Kw²

y = 2 × 3² = 2 × 9 = 18

Now for the right answer to the above question:

1. Option A is correct.
2. Option B is incorrect.
3. C is incorrect.
4. D is not the correct answer.

KEY-POINTS…

You may please note these/this:

• Write down the proportionality equation,
• Remove the sign of proportionality and introduce a constant,
• Solve for this constant and use it to do subsequent calculations. These are the steps.

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/ culled from 2015 JAMB-UTME mathematics past question 49 /