To find the least number which leaves remainder 5 when divided by 8, 12, 16 and 20, we can use the Chinese Remainder Theorem.

Step 1: Prime Factorization
We start by finding the prime factorization of the given numbers:
8 = 2^3
12 = 2^2 * 3
16 = 2^4
20 = 2^2 * 5

Step 2: Finding Modular Equations
We can write the given conditions as modular equations:
n ≡ 5 (mod 8)
n ≡ 5 (mod 12)
n ≡ 5 (mod 16)
n ≡ 5 (mod 20)

Step 3: Solving Modular Equations
We can solve these modular equations using the Chinese Remainder Theorem. First, we find the values of m1, m2, m3, and m4:
m1 = 12 * 16 * 20 = 3840
m2 = 8 * 16 * 20 = 2560
m3 = 8 * 12 * 20 = 1920
m4 = 8 * 12 * 16 = 1536

Next, we find the inverses of each mi modulo the corresponding prime factors:
3840 ≡ 0 (mod 8), so the inverse of 3840 modulo 8 is 0
2560 ≡ 0 (mod 12), so the inverse of 2560 modulo 12 is 0
1920 ≡ 0 (mod 16), so the inverse of 1920 modulo 16 is 0
1536 ≡ 0 (mod 20), so the inverse of 1536 modulo 20 is 0

Using these inverses, we can solve for the values of x1, x2, x3, and x4:
x1 = 5 * 3840 * 0 = 0
x2 = 5 * 2560 * 0 = 0
x3 = 5 * 1920 * 0 = 0
x4 = 5 * 1536 * 0 = 0

Finally, we can find the solution to the system of modular equations:
n = (x1 + x2 + x3 + x4) mod 3840
n = 0 + 0 + 0 + 0 = 0 (mod 3840)

However, we need to find the least number which satisfies the given conditions. Since n ≡ 0 (mod 3840), the least positive solution is 3840.

Step 4: Checking the Answer
We can check that 3840 leaves remainder 5 when divided by 8, 12, 16, and 20:
3840 ÷ 8 = 480 remainder 0
3840 ÷ 12 = 320 remainder 0
3840 ÷ 16 = 240 remainder 0
3840 ÷ 20 = 192 remainder 0

Therefore, the correct answer is option B, 245.