1. Let X = {n eN:0 < n < 999} be the set of all numbers with three or fewer digits. Define the function f : X → N by f(abc) = a + b + c, where a, b, and c are the digits of the number in X (write numbers less than 100 with leading O's to make them three digits). For example, f(253) = 2 +5 + 3 = 10. (a) Let A = {n € X : 113 < n < 122}. Find f(A). (b) Find f-'({1,2}) %3D (c) Find f-1(3). (d) Find f-'(28). (e) Is f injective? Explain. (f) Is f surjective? Explain.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Let X  {n ∈ N : 0 ≤ n ≤ 999} be the set of all numbers with three

or fewer digits. Define the function f : X → N by f (abc)  a + b + c,

where a, b, and c are the digits of the number in X (write numbers less

than 100 with leading 0’s to make them three digits). For example,

f (253)  2 + 5 + 3  10.

(a) Let A  {n ∈ X : 113 ≤ n ≤ 122}. Find f (A).

(b) Find f

−1

({1, 2})

(c) Find f

−1

(3).

(d) Find f

−1

(28).

(e) Is f injective? Explain.

(f) Is f surjective? Explain.

14. Let X = {n e N :0 < n < 999} be the set of all numbers with three
or fewer digits. Define the function f : X → N by f(abc) = a + b + c,
where a, b, and c are the digits of the number in X (write numbers less
than 100 with leading O's to make them three digits). For example,
f(253) = 2+5+ 3 = 10.
(a) Let A = {n € X : 113 < n < 122}. Find f(A).
(b) Find f-1({1,2})
(c) Find f-'(3).
(d) Find f-1(28).
(e) Is f injective? Explain.
(f) Is ƒ surjective? Explain.
Transcribed Image Text:14. Let X = {n e N :0 < n < 999} be the set of all numbers with three or fewer digits. Define the function f : X → N by f(abc) = a + b + c, where a, b, and c are the digits of the number in X (write numbers less than 100 with leading O's to make them three digits). For example, f(253) = 2+5+ 3 = 10. (a) Let A = {n € X : 113 < n < 122}. Find f(A). (b) Find f-1({1,2}) (c) Find f-'(3). (d) Find f-1(28). (e) Is f injective? Explain. (f) Is ƒ surjective? Explain.
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