# CAT Practice : Exponents and Logarithms

## Value of x

Q.13: 46+12+18+24+…+6x = (0.0625)-84, what is the value of x?
1. 7
2. 6
3. 9
4. 12

Choice A. 7

## Detailed Solution

Take right side expression
(0.0625)-84 = $\frac{1}{16}$-84

= (4-2)-84
= 4168

Take left side expression
46+12+18+24+…+6x = 46(1+2+3+4+x)
= 46 * 4(1+2+3+4+x)
= 46 * 4$\frac{x(x+1)}{2}$ (using the formula for sum of natural numbers from 1 to x)

Equating left and right side expresssions, we get 46 * 4$\frac{x(x+1)}{2}$ = 4168
Or 46 * 4$\frac{x(x+1)}{2}$ = 46*28
==> $\frac{x(x+1)}{2}$ = 28
or x(x+1) = 56

Solving for x we get, x = 7

Correct Answer: Choice (A)

## Our Online Course, Now on Google Playstore!

### Fully Functional Course on Mobile

All features of the online course, including the classes, discussion board, quizes and more, on a mobile platform.

### Cache Content for Offline Viewing

Download videos onto your mobile so you can learn on the fly, even when the network gets choppy!

## More questions from Exponents and Logarithms

With every extra hour you log in for this topic, it becomes exponentially simpler.