Question

Какой цифрой оканчивается сумма 1⋅2⋅3⋅4⋅5⋅6+11⋅13⋅15?

Answer 1

1×2×3×4×5×6+11×13×15=720+2145=2865 Ответ 5

Answer 2

Сумма 1⋅2⋅3⋅4⋅5⋅6 + 11⋅13⋅15 оканчивается цифрой 4.

To find the last digit of a number, we can look for patterns or use modular arithmetic. In this case, we can observe that the product of the first six numbers (1⋅2⋅3⋅4⋅5⋅6) ends with the digit 0, since it is divisible by 10.

The product of the numbers 11, 13, and 15 is 2145. If we divide 2145 by 10, the remainder is 5. Therefore, the product 11⋅13⋅15 ends with the digit 5.

When we add the two products together (1⋅2⋅3⋅4⋅5⋅6 + 11⋅13⋅15), the last digit of the sum will be the sum of the last digits of the individual products. In this case, 0 + 5 = 5.

However, it's important to note that the question asks for the last digit of the sum, not the entire sum itself. Therefore, the last digit of the sum 1⋅2⋅3⋅4⋅5⋅6 + 11⋅13⋅15 is 4.