Help with Indices question! (1 Viewer)

[Constantspy977]

Does anyone know how to do this question? I'm in year 8, but not sure how to do it, I feel like its simple but I just can't think of any way to do it. I got an answer but I'm just not sure Im correct, is it B? Even if I'm right or wrong, could you guys drop your methods because I feel like mine was time wasting and really impractical, much appreciated

How many digits are there in the answer for when this answer is written without indices?

(A) 122
(B) 123
(C) 124
(D) 243

 

[B1andB2]

2^120 x 5^120 x 5^3
= (2x5)^120 x 5^3
= 10^120 x 125

so after 125 you get 120 zeros

so i agree with B)

 

[CM_Tutor]

​

This number has 123 digits - 125 followed by 120 zeroes.

Edit to add, after cross-posting: So, I agree with @B1andB2, the answer is B.

 

[Constantspy977]

2^120 x 5^120 x 5^3
= (2x5)^120 x 5^3
= 10^120 x 125

so after 125 you get 120 zeros

so i agree with B)

is there a way to do it without a calculator?

 

[B1andB2]

is there a way to do it without a calculator?

you don't need a calculator for those steps

 

[Constantspy977]

​

This number has 123 digits - 125 followed by 120 zeroes.

Edit to add, after cross-posting: So, I agree with @B1andB2, the answer is B.

oh ok thanks!

 

[Constantspy977]

you don't need a calculator for those steps

man, now I feel stupid :/ it was a really easy question :/

 

[B1andB2]

man, now I feel stupid :/ it was a really easy question :/

noo all g it's fine it doesn't even look simple with all those powers tbh. No need to feel ashamed.

 

[Constantspy977]

noo all g it's fine it doesn't even look simple with all those powers tbh. No need to feel ashamed.

yeah ig, well at least ik how to do it now

 

[CM_Tutor]

It is a regular, though infrequent, idea that appears in maths exams - how to handle numbers that are beyond the range of a calculator. The trick here, as always, is to isolate powers of 10, that only move decimal points, and handle them manually. You may not have spotted that there were a whole lot of powers of 10 hidden in this calculation, but if you learn from it that looking for powers of 10 is a useful technique at times, then you have benefited from not only your mistake, but also from your wisdom in seeking help.

 

[Constantspy977]

It is a regular, though infrequent, idea that appears in maths exams - how to handle numbers that are beyond the range of a calculator. The trick here, as always, is to isolate powers of 10, that only move decimal points, and handle them manually. You may not have spotted that there were a whole lot of powers of 10 hidden in this calculation, but if you learn from it that looking for powers of 10 is a useful technique at times, then you have benefited from not only your mistake, but also from your wisdom in seeking help.

Hey! Thanks man it means a lot!