Eight Tens 2018 5Add39
1. **Stating the problem:** Use exactly eight "10" numbers and the operations +, -, ×, ÷, and brackets to form an expression equal to 2018.
2. **Understanding the constraints:** We can only use the number 10 eight times and the basic arithmetic operations with brackets.
3. **Strategy:** Try to build numbers close to 2018 by combining 10s cleverly, for example, by forming 100 or 1000 using multiplication and addition.
4. **Constructing 2018:**
- Note that 2018 = 2000 + 18
- 2000 can be formed as 20 × 100
- 20 = 10 + 10 (uses 2 tens)
- 100 = 10 × 10 (uses 2 tens)
- So 20 × 100 uses 4 tens
- 18 can be formed as 10 + 8, but 8 is not directly from 10s, so try 18 = 10 + 10 - 2 (need to form 2)
- 2 can be formed as (10 ÷ 10) + (10 ÷ 10) (uses 4 tens)
5. **Counting tens:**
- 20 = (10 + 10) uses 2 tens
- 100 = (10 × 10) uses 2 tens
- 2 = (10 ÷ 10) + (10 ÷ 10) uses 4 tens
- 10 + 10 - 2 uses 2 tens + 2 tens + 4 tens = 8 tens total, but we need to check carefully.
6. **Final expression:**
$$2018 = (10 + 10) \times (10 \times 10) + 10 + 10 - ((10 \div 10) + (10 \div 10))$$
7. **Verification:**
- (10 + 10) = 20 (2 tens)
- (10 × 10) = 100 (2 tens)
- 20 × 100 = 2000
- 10 + 10 = 20 (2 tens)
- (10 ÷ 10) + (10 ÷ 10) = 1 + 1 = 2 (4 tens)
- So total tens used: 2 + 2 + 2 + 4 = 10 tens, which is too many.
8. **Adjust to use exactly 8 tens:**
Try to form 18 as 10 + 10 - (10 ÷ 10) - (10 ÷ 10) which uses 4 tens.
9. **Expression:**
$$2018 = (10 + 10) \times (10 \times 10) + 10 + 10 - (10 \div 10) - (10 \div 10)$$
10. **Counting tens:**
- (10 + 10) = 2 tens
- (10 × 10) = 2 tens
- +10 +10 = 2 tens
- - (10 ÷ 10) - (10 ÷ 10) = 2 tens
Total = 2 + 2 + 2 + 2 = 8 tens
11. **Calculate:**
- (10 + 10) = 20
- (10 × 10) = 100
- 20 × 100 = 2000
- 10 + 10 = 20
- (10 ÷ 10) = 1
- So 2000 + 20 - 1 - 1 = 2018
**Final answer:**
$$2018 = (10 + 10) \times (10 \times 10) + 10 + 10 - (10 \div 10) - (10 \div 10)$$