Question

Tính Tổng

a)215+217+219+221+223

b)S=2*10+2*12+2*14+...+2*20

 

Answer 1

a: \(=\left(215+223\right)+\left(217+221\right)+219=418+418+219=219\cdot5=1095\)

b: \(S=2\left(10+12+14+16+18+20\right)\)

\(=2\cdot30\cdot3=6\cdot30=180\)

Answer 2

`= (215 + 223) + (217 + 221) + 219`

`= 219 xx 2 + 219 xx 2 + 219`

`= 219 xx 5`

`= 1095`

`b, = 2 xx (10 + 12 + ... +20)`

`= 2 xx (20+10) xx ((20-10) :2 + 1) : 2 = 180`.

Answer 3

a) Tổng là

\(\left(223+215\right).5:2=1095\)

b) Có: \(S=2.10+2.12+...+2.20\)

\(\Rightarrow S=2\left(10+12+14+...+20\right)\)

\(\Rightarrow S=2\left[\left(20+10\right).6:2\right]=180\)