The moment of inertia of a spherical shell is I = mr²
If two spheres have the same moment of inertia, then
I₁ = I₂
m₁(r₁)² = m₂(r₂)²
Solve for the second mass:
m₂ = m₁ (r₁/r₂)²
Given m₁ = 1 kg, r₁ = 2 m, r₂ = 1m,
m₂ = (1 kg) (2 m / 1 m)² = 4 kg
The calendar obviously has an integral number of years and months in 400 years. If it has an integral number of weeks, then it will repeat itself after that time. The rules of the calendar eliminate a leap year in 3 out of the four century years, so there are 97 leap years in 400 years. The number of excess days of the week in 400 years can be found by ...
(303·365) mod 7 + (97·366) mod 7 = (2·1 + 6·2) mod 7 = 14 mod 7 = 0
Thus, there are also an integral number of weeks in 400 years.
The first day of the week is the same at the start of every 400-year interval, so the calendar repeats every 400 years.
Rewrite 7/8 as a decimal by dividing 7 by 8:
7/8 = 0.875
Now to find how much further she has to run subtract where is now from the total distance:
0.875 - 0.3 = 0.575
She needs to run 0.575 miles more
She can buy 3 tubes be cause 8.50 time 2 is less then 20$ but 8.50 times three is more than 20$ its 25.5
