Aptitude - Ratio and Proportion - Discussion

Discussion Forum : Ratio and Proportion - General Questions (Q.No. 13)

Ratio and Proportion

13.

The fourth proportional to 5, 8, 15 is:

Answer: Option

Explanation:

Let the fourth proportional to 5, 8, 15 be x.

Then, 5 : 8 : 15 : x

5x = (8 x 15)

x =	(8 x 15)	= 24.
	5

Discussion:

34 comments Page 1 of 4.

Jaskaran said: 1 decade ago

How come 5x ? Please explain in detail.

Malli said: 1 decade ago

There is 5:8:15:x then as for formula
1st x 4th=2nd x 3rd
i.e 5*x=8*15(it is a formula)
there four x=24

Manik said: 1 decade ago

Is this formula applicable for such other problems? What abt the formula of fifth, sixth or higher proportional?

Sai said: 1 decade ago

Formula must be used compulsory ? we can assume it as in series form as 5, 15, 25, 35.... In same manner 8, 18, 28......

Shrishti said: 1 decade ago

This is solved by proportional formula such as a:b :: c:d

Formula: a*d=b*c (as said find fourth proportional).

Reethrose said: 1 decade ago

5:8::15:?
5*3=15
8*3=24
so the answer is 24.

Priyankapatil said: 1 decade ago

How to find fifth proportional?

Azeem said: 1 decade ago

Assume a=5, b=8, c=15.

We all know the ad = bc.

a = bc/d, b = ad/c, c = ad/b.

Simillarly d = bc/a.

So 8*15/5 => 120/5 = 24.

Divya said: 1 decade ago

Let the 4th proportional to 5:8::15:x.

Product of extremes = product of means.

5x = 8*15.

x = 120/5.

= 24.

Hanson said: 1 decade ago

Better still:

It will be split this way: 5:8=> 15:x.

Hence, the common factor is 15/5 = 3.

Thus, x/8 = 3.

x= 8*3 =24.

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