if 10 have the same pace, and 10 of them do it in 16 hr, then each alone will do it in 160hr

now the question is how much time will it take to 8 machines with rate of 160 hr to do the job

Try this:

3^x-1 = (3^x)/3

3^x - 3^x-1 = 3^x - (3^x)/3 = (2 * 3^x)/3 = 162

=> x = ...

note that they say MUST true, not possibly true

and because we get:

xy + z = xy + xz

xz = z

only 5. must be true

answer

the average of the series is 4
the standard deviation is: sqrt [(40)/5] = sqrt [8]

we would like the new sum to be ~56 to get sqrt[8] so the closest will be:

2 and 6 then the standard deviation would be: sqrt[48/7]

D

4C1 + 4C3 = 8

x = 13!

a = x^16 - x^8 / x^8 + x ^ 4 =

(x^8+x^4)(x^8-x^4)/(x^8+x^4) =

x^8 - x^4

a/x^4 =

x^4 - 1

digit number of 13! must be 0 because its like (1*2*3...*11*12*13) * 10

so the final answer would be 1

but arent you repeating on options like this? this is what's confusing, i dont think you can just multiply (13^4) by 48*47 lets take 1,2,3 of type hart and 4,5,6 of 3 different types, so: {1,4,5,6} {2,3} {2,4,5,6} {1,3} {3,4,5,6} {2,1} are the same choises, you have here a very large number of repet...