You can get the tens digit of any number <em>n</em> by computing the quotient
(<em>n</em> (mod 100)) / 10
and ignoring the remainder.
Taking the given sum (mod 100) gives
7! + 8! + … + 2006! ≡ 7! + 8! + 9! (mod 100)
since the last 1997 terms (i.e. 10! up to 2006!) in the sum are multiples of 100. That is,
• every term beyond 100! is obviously a multiple of 100
• every term beyond 25! contains a factor of both 4 and 25
• every term beyond 10! contains two factors each of both 2 and 5 (i.e. every factorial term contains 4, 5, and 10)
The remaining sum is easy to compute by hand:
7! + 8! + 9! = 7! (1 + 8 + 8 × 9) = 5040 × 81 = 408,240
so the tens digit is 4.
B. 28 is 4x7 and 20 is 5x7 which means it fits the 7:5 requirement and most importantly 28+28+20+20 is 56+40 and that equals 96
Answer:
5/3
Step-by-step explanation:
5×(10×1/3)
=10×5/3
=since 5×(10×1/3) gives 50/3 so thus 10×5/3.
The fraction is therefore 5/3
I did the calculations two ways. The last data item was 185.00!
I wasn't sure if this was correct or a typo. With 185.00: mean 33.31. STD dev 53.68. With 185.00 changed to 18.50: mean 14.81 std dev 2.75
