Question

Tính

a) 1 + 7 + 8 + 15 + 23 + ... + 160

b) 1 + 4 + 5 + 9 + 14 + ... + 60 + 97

c) 78.31 + 78.24 + 78.17 + 22.72

Answer 1

\(a.1+7+8+15+23+...+160\)

\(=1+\left(8-1\right)+\left(15-7\right)+\left(23-8\right)+...+\left(160-61\right)+\left(259-99\right)\)

\(=-7+160+259\)

\(=412\)

Answer 2

\(b.1+4+5+9+14+...+60+97\)

\(=1+4+5+9+14+23+37+60+97\)

\(=5+5+23+23+97+97\)

\(=2\left(5+23+97\right)\)

\(=2.125\)

\(=250\)

Answer 3

\(c.78.31+78.24+78.17+22.72\)

\(=78\left(31+24+17\right)+22.72\)\(=78.72+22.72\)\(=72\left(78+22\right)\)\(=72.100\)\(=7200\)

Answer 4

a, 1+7+8+15+23+...+160

= 1+(8-1)+(15-7)+(23-8)+...+(160-61)+(259-99)

=7+160+259

=412

Answer 5

 

c) 78.31 + 78.24 + 78.17 + 22.72

= 78.(31+24+17).22.72

= 78.72+22.72

= 72.(78+22)

=72.100

=7200.

Answer 6

a) \(1+7+8+15+23+...+160\)

\(=1+\left(8-1\right)+\left(15-7\right)+\left(23-18\right)+...+\left(160-61\right)+\left(259-99\right)\)

\(=-7+150+259\)

\(=412\)

Chúc bạn học tốt!!!