Find the remainder when
`1661 + 1551 + 1441 + 1331 + 1221` is divided by 20.

Answer

To find the remainder when \( 1661 + 1551 + 1441 + 1331 + 1221 \) is divided by 20, we can follow these steps:

### Step 1: Calculate the remainders of each number when divided by 20.
- For \( 1661 \):
\[ 1661 \div 20 = 83 \quad \text{(integer part)} \]
\[ 20 \times 83 = 1660 \]
\[ 1661 - 1660 = 1 \quad \text{(remainder)} \]

- For \( 1551 \):
\[ 1551 \div 20 = 77 \]
\[ 20 \times 77 = 1540 \]
\[ 1551 - 1540 = 11 \quad \text{(remainder)} \]

- For \( 1441 \):
\[ 1441 \div 20 = 72 \]
\[ 20 \times 72 = 1440 \]
\[ 1441 - 1440 = 1 \quad \text{(remainder)} \]

- For \( 1331 \):
\[ 1331 \div 20 = 66 \]
\[ 20 \times 66 = 1320 \]
\[ 1331 - 1320 = 11 \quad \text{(remainder)} \]

- For \( 1221 \):
\[ 1221 \div 20 = 61 \]
\[ 20 \times 61 = 1220 \]
\[ 1221 - 1220 = 1 \quad \text{(remainder)} \]

### Step 2: Sum the remainders.
Now we add the remainders we calculated:
\[ 1 + 11 + 1 + 11 + 1 = 25 \]

### Step 3: Find the remainder of the sum when divided by 20.
Now, we divide the sum \( 25 \) by \( 20 \):
\[ 25 \div 20 = 1 \quad \text{(integer part)} \]
\[ 20 \times 1 = 20 \]
\[ 25 - 20 = 5 \quad \text{(remainder)} \]

### Final Answer:
The remainder when \( 1661 + 1551 + 1441 + 1331 + 1221 \) is divided by 20 is \( 5 \).

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