*START WITH ONE FOURTH (1/4) OF 20. *ADD TWO FOURTHS (2/4) OF 20.

*ADD THREE FOURTHS (3/4) OF 20.

WHAT NUMBER AM I?

What's the difference between: x≥0 and nonnegative integer. ?

Adrawer contains 12 identical white socks, 18 identical black socks and 14 identical brown socks. what is the least number of socks you must choose, without looking, to be certain that you have chosen two socks of the same colour?

Prove that 16^4-2^13-4^5 is divisible by 11.