Aptitude - Boats and Streams - Discussion

72x x 60 = 90 (100 - x2)

x2 + 48x + 100 = 0

How this step comes? pls tell me.

Hi there,

I dont understand from where the 60 comes. is it a concept or derived from theose data? pls explain.

You should multiply (10 - x) and (10 + x) as to take LCM, so that you can substract the numeraters i.e. 36-36.

You knew that (a+b) x (a-b) = (a2 - b2) , (NOTE: read it as a square minus b square.)

And in order to multiply the denominators you got to multiply them with the numerators also; so, you get 36(10+x) - 36 (10-x), this is divided by (100 - x2 -i.e.square)

But what i do not understand is from where does that 60 come?

Anyone?

60 is to convert min to hour.

Why we should convert min to hour anybody?

Because the unit is in hours.

Can any body explain this?

A boat takes 90 minutes "less" to travel. Then why do we write the equation = 90?

we can also take like that....
it is easy to form eqn like above
ie difference between upstream and downsttream
..

I didn't get from wer did the 60/90 ratio come! can anybody?

Downstream speed = (upstream speed-90); _____(because downstream takes 90 min less then upstream.)

Hence, (90/60)min=(36/(10-x))+(36/(10+x));

and proceed as given in solution i.e. simplify the equation.

Given Condition:(upstream speed-(90/60)min)=downstream speed;

we know,
time=distance/speed;

(90/60)min=(upstream distance/upstream speed)+
(downstream distance/downstream speed)

(90/60)min=(36/(10-x))+(36/(10+x));