Aptitude - Square Root and Cube Root - Discussion

Discussion :: Square Root and Cube Root - General Questions (Q.No.10)

10. 

If 5 = 2.236, then the value of 5 - 10 + 125 is equal to:
2 5

[A]. 5.59
[B]. 7.826
[C]. 8.944
[D]. 10.062

Answer: Option B

Explanation:

5 - 10 + 125 = (5)2 - 20 + 25 x 55
2 5 25

= 5 - 20 + 50
25

= 35 x 5
25 5

= 355
10

= 7 x 2.236
2

= 7 x 1.118

= 7.826


Mannoj Kumar said: (Jun 12, 2011)  
Another method
=sq5[ 1/2 - 10/5+ 5]
=2.236[ 0.5 -2 + 5]
=2.236 * 3.5
=7.82600

Anuj said: (Jul 30, 2011)  
How you calculate 10/5 ?

M.V.Krishna/Palvoncha said: (Sep 11, 2011)  
Hello Anuj.

root=r.

Given (r5/2)-(10/r5)+r125.

10/r5 = 2*5/r5 = 2r5.

r125 = 5r5

(r5/2)-2r5+5r5

(r5/2)+3r5

(r5+6r5)/2

7r5/2

Subst. given r5 value we get 7.826.

Hope you understood.

Radhika said: (Apr 16, 2012)  
Why we multiply with squreroot 5 on both sides.

Avinash said: (Mar 22, 2014)  
rt5/2 - 10/rt5 + rt125.

Just put value of rt5 and calculate.

2.236/2 - 10/2.236 + 5*2.236 = 7.826.

It's simple.

Tejas said: (Oct 2, 2014)  
How it come 2 root 5?

Shradha said: (Aug 31, 2015)  
No need to multiply root five to both side.

Kanchan said: (Jan 17, 2016)  
How to solve root?

Vipinkumar said: (Jul 23, 2016)  
You are right @Mannoj Kumar.

@Anuj.

If we take common term sqrt(5) from each term so that we get;

In first term: sqrt 5[ 1/2 ].
In second term: sqrt5 [10/((sqrt5)/sqrt5)] = sqrt5[10/(sqrt5 * sqrt5)]
= sqrt5[10/5].

In third term: sqrt5[(5 * sqrt5)/sqrt5] = sqrt5[5].

In these three terms, sqrt5 is common and take it outside the bracket and apply it in the expression(question)so we get.

= sq5[ 1/2 - 10/5 + 5].
= 2.236[ 0.5 -2 + 5].
= 2.236 * 3.5.
= 7.82600.

Kongkon said: (Feb 18, 2017)  
I don't understand. Can anyone explain me please?

Sri Satya Kanamarlapudi said: (May 31, 2018)  
It can be also rewritten as (√(5) √(5)/2) - (2*√(5)√(5)/√(5))+(5*√(5)).

√(5)/2 - 2√(5) +5√(5).
7√(5)/2 = 7.826.

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