Điền số thích hợp vào ô trống. + Số các số tự nhiên x sao cho x chia hết cho 5 và 386leqslant xleqslant 396 là square + Số các số tự nhiên n sao cho n chia hết cho cả 2 và 5 biết 252leqslant nleqslant 287 là square

1. The question asks for the number of natural numbers \( x \) that are divisible by 5 and lie in the range \( 386 \leq x \leq 396 \). To find this, we can use the formula for finding the number of terms in an arithmetic sequence: \( n = \frac{{\text{last term} - \text{first term}}}{\text{common difference}} + 1 \). In this case, the first term is 386, the last term is 396, and the common difference is 5. Plugging these into the formula, we get \( n = \frac{{396 - 386}}{5} + 1 = 11 \). <br /> 2. The question asks for the number of natural numbers \( n \) that are divisible by both 2 and 5 and lie in the range \( 252 \leq n \leq 287 \). A number that is divisible by both 2 and 5 must be divisible by 10. Using the same formula for finding the number of terms in an arithmetic sequence, the first term is 252, the last term is 287, and the common difference is 10. Plugging these into the formula, we get \( n = \frac{{287 - 252}}{10} + 1 = 10 \).