Answer:

1. 20 for $1.56 =A. 7.8 cents each

2. $3.78 for 6=B. 63 cents each

3.  2frac{1}{2} or one dollar =C. 40 cents each

4. 5 at $3.90 = D. 78 cents each

5. 1frac{1}{2} for $1.58 = E. $1.05 each

Step-by-step explanation:

1.   20 for $1.56

Since cost of 20 items = $1.56

So, cost of 1 item = frac{1.56}{20}

                            =$0.078

1 dollar = 100 cents

So, $0.078= 0.078 * 100 =7.8 cents.

2. $3.78 for 6

Since cost of 6 items = $3.78

So, cost of 1 item = frac{3.78}{6}

                            =$0.63

1 dollar = 100 cents

So, $0.63 = 0.63 * 100 =63 cents.

3. 2frac{1}{2} for one dollar

Cost of 2frac{1}{2}=frac{5}{2} = $1

So, cost of 1 item =  frac{1}{frac{5}{2}}

                             = frac{2}{5}

1 dollar = 100 cents

So, $frac{2}{5}=frac{2}{5}times100 =40 cents.

4. 5 at $3.90

Since cost of 5 items = $3.90

So, cost of 1 item = frac{3.90}{5}

                            =$0.78

1 dollar = 100 cents

So, $0.78= 0.78 * 100 =78 cents.

5. 1frac{1}{2} for $1.58

Cost of 1frac{1}{2}=frac{3}{2} = $1.58

So, cost of 1 item =  frac{1.58}{frac{3}{2}}

                             = 1.05

Thus,

1. 20 for $1.56 =A. 7.8 cents each

2. $3.78 for 6=B. 63 cents each

3.  2frac{1}{2} or one dollar =C. 40 cents each

4. 5 at $3.90 = D. 78 cents each

5. 1frac{1}{2} for $1.58 = E. $1.05 each