arkle wrote:

Bunuel Now I understand that plugging in numbers is the most efficient way to solve this question.However, while giving the test, I ventured on this journey to try to substitute t or r in one equation or other.I was unable to come to an answer. Would appreciate of you throw some insight. My equations were -

r(t+4)=60

(r+5)t=80

My r and t came out to be fractions and not integers. Wondering what am I doing wrong?

Hi

arkle,

Your equations are perfectly fine. I am presuming you made a calculation mistake while solving them. Let me briefly break it down step wise for you.

\(r(t+4)=60\) i.e. \(rt + 4r = 60\)...... Eqn 1

\((r+5)t=80\) i.e. \(rt + 5t = 80\).......Eqn 2

Eqn 1 - Eqn 2 would give us \(5t - 4r = 20\) i.e.

\(r = \frac{5t - 20}{4}\)...... Eqn 3

Substituting value of r from Eqn 3 in Eqn 1, we get

\(\frac{5t -20}{4}* (t + 4) = 60\)

\(5t^2 = 320\) i.e. \(t^2 = 64\)

Since \(t\) can't have a negative value, \(t = 8\) seconds which is the time taken by bird to fly from antenna to window pane.

We are asked in the question to find the time taken by bird to fly from nest to antenna i.e. \(t + 4 = 12\) seconds.

Hope its clear

Regards

Harsh

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