Aptitude - Surds and Indices - Discussion

Discussion :: Surds and Indices - General Questions (Q.No.4)

4. 

If 5a = 3125, then the value of 5(a - 3) is:

[A]. 25
[B]. 125
[C]. 625
[D]. 1625

Answer: Option A

Explanation:

5a = 3125       5a = 55

a = 5.

5(a - 3) = 5(5 - 3) = 52 = 25.


Girish said: (Jun 18, 2011)  
Also 5a-3 = 5a/53 = 3125/125 = 25

Girish said: (Jun 18, 2011)  
Above can be read as 5^a-3 = 5^a/5^3 = 3125/125 = 25

Shridhar Naik said: (Sep 16, 2012)  
5^(a-3)=5^a*5^(-3)=3125/125=25

Bisu said: (May 27, 2013)  
Also can be solved.

5^a = 3125.

5^(a-3) = ?

==>5^(a-3) = 5^a/5^3 = 3125/125 = 25.

Veronika said: (Jan 11, 2017)  
I am very new to this, what does ^ mean?

I really need help.

Swapnil said: (Jan 12, 2017)  
5 a-3 = 5^a/5^3.
= 3125/125.
= 25.

Shalini said: (Apr 27, 2017)  
@Veronika:

^ means raise to the power, i.e. 5^a= 5 raise to the power a.

Ayesha said: (May 9, 2017)  
Why in the question they have to ask 5a they should have directly written it as 5^a did they get the same meaning?

Please, someone tell me.

Babu Vijayendra Kumar said: (Jun 26, 2017)  
I'm not getting this, anybody explain the logic.

Aditya said: (Jul 22, 2017)  
5a=3125 we can write 3125 in 5 * 5 * 5 * 5 * 5 then we get 5 power 5 then put value.

Then, we get 5 power 2 we get 25.

Ramesha T S said: (Oct 15, 2017)  
5^(a-3)=(5^a)/(5^3)=3125/(5*5*5) = 25.

Mandeep Mehra said: (Sep 15, 2018)  
5^a=3125.
5^a-3=5^a/5^3.
5^a/5^3=3125/125=25.

Asra said: (Apr 13, 2019)  
How to get the value of a by 5^a= 3125?

Someone please help.

Dhika said: (May 15, 2019)  
Here, the value of 5^a=3125.

Urvashi said: (Jul 22, 2020)  
Given that 5^a = 3125
5^a = (5*5*5*5*5)
Since (5*5*5*5*5) = 3125.

So, 5 power a = 5 power 5.
Since bases are same!
Then subtract 3 from each according to question!
5^(a-3) = 5^(5-3),
5^(a-3) = 5^2,
5^(a-3) = (5*5).
5^(a-3) = 25.

Siddharth Sahu said: (Jul 24, 2021)  
The simple method is 5^a/5^3 = 3125/5^3.
That is equal to 5^a-3=3125/125 = 25.

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