# Aptitude - Surds and Indices - Discussion

Discussion Forum : Surds and Indices - General Questions (Q.No. 4)
4.
If 5a = 3125, then the value of 5(a - 3) is:
25
125
625
1625
Explanation:

5a = 3125       5a = 55

a = 5.

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

Discussion:
18 comments Page 1 of 2.

Muhammad shahid said:   3 weeks ago
As we know;

5^a = 3125.
3125 = 5^5.
5^a = 5^5.

So. comparing power
a = 5
5^(a-3)
put a = 5
5^(5-3)
5^2 = 25
So, 25 is the correct answer.

Tari said:   2 years ago
I am not getting this. Please explain me in detail.
(1)

Siddharth sahu said:   3 years ago
The simple method is 5^a/5^3 = 3125/5^3.
That is equal to 5^a-3=3125/125 = 25.
(3)

Urvashi said:   4 years ago
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.
(2)

Dhika said:   5 years ago
Here, the value of 5^a=3125.

Asra said:   5 years ago
How to get the value of a by 5^a= 3125?

(1)

Mandeep Mehra said:   6 years ago
5^a=3125.
5^a-3=5^a/5^3.
5^a/5^3=3125/125=25.

RAMESHA T S said:   7 years ago
5^(a-3)=(5^a)/(5^3)=3125/(5*5*5) = 25.

Aditya said:   7 years ago
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.

Babu vijayendra kumar said:   7 years ago
I'm not getting this, anybody explain the logic.
(2)