hành động là: đang nhảy

1 người nói là: hay quá

ticks cho mình nhé

3×43​+4×53​+…+98×993​+99×1003​

\(= 3 \times \left(\right. \frac{1}{3 \times 4} + \frac{1}{4 \times 5} + \hdots + \frac{1}{98 \times 99} + \frac{1}{99 \times 100} \left.\right)\)

\(= 3 \times \left(\right. \frac{1}{3} - \frac{1}{4} + \frac{1}{4} - \frac{1}{5} + \hdots + \frac{1}{98} - \frac{1}{99} + \frac{1}{99} - \frac{1}{100} \left.\right)\)

\(= 3 \times \left(\right. \frac{1}{3} - \frac{1}{100} \left.\right)\)

\(= 1 - \frac{3}{100} = \frac{97}{100}\)

1×32​+3×52​+5×72​+⋯+15×172​

\(= \frac{1}{1} - \frac{1}{3} + \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7} + \hdots + \frac{1}{15} - \frac{1}{17}\)

\(= \frac{1}{1} - \frac{1}{17} = \frac{16}{17}\)

1. goes

2. is running

3. is crying

4. travel

6 tạ

A=11​−21​+21​−31​+31​−41​+⋯+981​−991​+991​−1001​

\(A = \frac{1}{1} = \frac{1}{100} = \frac{99}{100}\)

b) Đặt \(B = \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{32} + \frac{1}{64} + \frac{1}{128}\)

\(2 \times B = \left(\right. \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{32} + \frac{1}{64} + \frac{1}{128} \left.\right) \times 2\)

\(2 B = 1 + \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{32} + \frac{1}{64}\)

\(2 B - B = \left(\right. 1 + \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{32} + \frac{1}{64} \left.\right) - \left(\right. \frac{1}{2} + \frac{1}{4} + \frac{1}{8} + \frac{1}{16} + \frac{1}{32} + \frac{1}{64} + \frac{1}{128} \left.\right)\)

\(B = 1 - \frac{1}{128} = \frac{127}{128}\)

Đổi: 4 tạ = 400kg; 40 yến = 400kg

Trung bình mỗi thửa ruộng thu hoạch được số kg ngô là:

(661 + 400 + 400) : 3 = 487 (kg)

Đáp số: 487kg ngô

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