Express the following ratio in simplest form:
21:9

Alake near the arctic circle is covered by a 222-meter-thick sheet of ice during the cold winter months. when spring arrives, the warm air gradually melts the ice, causing its thickness to decrease at a constant rate. after 333 weeks, the sheet is only 1.251.251, point, 25 meters thick. let s(t)s(t)s, left parenthesis, t, right parenthesis denote the ice sheet's thickness sss (measured in meters) as a function of time ttt (measured in weeks).

X+y=-4 x-y=2 use elimination with adding and subtraction

The? half-life of a radioactive substance is 20 years. if you start with some amount of this? substance, what fraction will remain in 120 ? years