let's find the area of the outer circle and the inside circle
the inside's circle area
A= π x 6²=36π
the outer's
A' = π x 4x²= 4πx²
A'-A=4πx²- 36π=160πcm² equivalent to x²- 9=40, so x²=49 implies x =sqrt(49)=7, x=7.
Answer:

Step-by-step explanation:
we know that
The circumference of a circle is equal to

where
D is the diameter
in this problem we have

substitute
-----> equation that give the value of the circumference

Answer:
I assume you know Arithmetic Progression .
so, we have to find the first and last 4-digit number divisible by 5
first = 1000 , last = 9990
we have a formula,
= a + (n-1)d
here,
is the last 4-digit number divisible by 5.
n is the number of 4-digit even numbers divisible by 5
d is the common difference between the numbers, which is 10 in this case
a is the first 4-digit number divisible by 5
9990 = 1000 + (n-1)*10
899 = n-1
n = 900
Hence, there are 900 4-digit even numbers divisible by 5
The 4th term is 135
n-1
you get it by using the formula Tn= ar <span />