Question

Find the fourth proportional to the given numbers 12, 15 and 28​

Answer 1

$\underline{\underline{\huge{\gray{\tt{\textbf Answer :-}}}}}$

$\:\:$

$\sf\large\bold{\orange{\underline{\blue{ Given :-}}}}$

$\:\:$

• First three proportionals 12 , 15 , 28

$\:\:$

$\sf\large\bold{\orange{\underline{\blue{ To \: Find :-}}}}$

$\:\:$

• The fourth proportional

$\:\:$

$\sf\large\bold{\orange{\underline{\blue{ Solution :-}}}}$

$\:\:$

Let the fourth proportional be "p"

$\:\:$

So,

$\:\:$

The proportion will be :

$\:\:$

➠ 12:15::28:p

$\:\:$

We know that ,

$\:\:$

Product of extremes = Product of means

$\:\:$

• Extremes - They are the outer most numbers on each side of a proportion. In the given proportion 12 & p are extremes

• Means - They are the inner numbers i.e lies in between the extremes. In the given proportion 15 & 28 are means

$\:\:$

• Extremes = 12 , p

• Means = 15 , 28

$\:\:$

So,

$\:\:$

➜ 12 × p = 15 × 28

$\:\:$

➜ 12p = 420

$\:\:$

➜ $\sf p = \dfrac { 420 } { 12 }$

$\:\:$

➨ p = 35

$\:\:$

• Hence the fourth proportional is 35

$\:\:$

Additional information

$\:\:$

In a proportion a:b::c:d

$\:\:$

• $\sf \dfrac { a } { b } = \dfrac { c } { d }$

$\:\:$