ratio/proportions
posted by rian .
a geologist found that silt was deposited on a river bed at the rate of 4cm every 170 years , how long would it take for 5 cm of silt how long would it to be deposited ???? plz helpp

4/170 = 5/x
Cross multiply and solve for x. 
I got 850/x and 4 /x what do I do next to get the answer

When we cross multiply, we multiply the first and last terms together. Then we multiply the two middle terms together.
4/170 = 5/x
4x = 850
Divide both sides by 4
x = 212.5 years
It'll take 212.5 years for 5 cm of silt to be deposited. 
thx u

You're welcome.