What number has the same value as 30 tens

Multiplication should be used here. 30 tens means number ten should be added 30 times. 10+10+...+10 thirty times, which can be written as 10 x 30 which gives us the number 300. We get the same answer if the value of 10 thirties is required. We can use the same way to get the answer like the question given in the begging.

If the diameter is 8 than the radius is 4 because 2r or 2*radius equals the diameter. 4*2=8. 8/2=4.