QZ wrote:

Bunuel wrote:

QZ wrote:

How many digits are in (8×10^14)(10×10^10)?

A. 24

B. 25

C. 26

D. 27

E. 28

Bunuel can you help me in this. Though I know the concept, still I am counting it as 27.

(8×10^14) ; 10^14 means fourteen "0s" and one "1" So total 15 digits ; 8 does not change the number of digits

(10×10^10) ; 10^11 means 12 digits

So 15+12 = 27

You cannot add like that. For example, 10 has 2 digits but 10*10 does not have 2 + 2 = 4 digits it has 3 digits.

You should do the following way: (8×10^14)(10×10^10) = 8*10^25 --> 10^25 has 26 digits. Multiplying it by 8 does not change the number of digits.

Answer: C.

Can we deduce that number less than 10 does not change the number of digits ever?

Hi..

You can't take that as a rule..

It depends on other factors too..

8*10^2.... 8 will not effect

8*20^2.... 8 will effect...

Why you have gone wrong is that you have separated the 10s..

(8*10^14)(10*10^11)....

Although you have correctly solved 10*10^11, you have added an extra digit of 1 from 10^14..

10*10^11 could have meant 10 - 2 digits and 10^10- 10 zeroesand 1 digit for '1', so 10+1=11 digits

Total 2+11=13digits.. but is it so ...NO

It is 12 digits because 10*10^10=10^11, meaning 12 digits

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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