"He starts both trains at the same time. Train A returns to its starting point every 12 seconds and Train B returns to its starting point every 9 seconds". Basically, what you need to do is find the least common multiple. The least common multiple of 12 and 9 is 36, so the least amount of time, in seconds, that both trains will arrive at the starting points at the same time is 36 seconds.
E. 3/12 is equivalent to 1/4, which is the ratio of the cylinders.
Each balloon string is 6ft , 6ft translates to two yards he’ll need 114 yards.
The formula for half-life is:

A is the amount remaining, P is the initial amount, t is the time that has passed, and h is the half-life of the substance. Plug in the values that you know and solve:

Rounded to the nearest whole number, the density of the substance was about 13<span>mg / cm².</span>