What is the subset of the letters in the word 'numbers'

Question

What is the subset of the letters in 'numbers'?

I thought it meant to make a word out of the letters in 'numbers' so I tried to make a word out of it, but I couldn't make a word and so I don't understand the task.

Please help me this is my homework. If I don't bring it to school by Friday I'll be put in detention for 5 hours.

Answer 1

When you say all letters are a-z, you can write the set of all letters as

$$\{a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z\}$$

The subset of all letters that are in the word "numbers" is

$$\{n,u,m,b,e,r,s\}$$

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Side note

There are much more letters:

• Greek alphabet: α, β, γ, ...
• Russian alphabet: а, б, в, г, д, ...
• Hebrew alphabet: א, ב, ג
• ...