Đáp án:
`A=36`
Giải thích các bước giải:
`A=70.((121212)/(565656)+(121212)/(727272) +(121212)/(909090))`
`A= 70. ((121212:40404)/(565656:40404) + (121212:121212)/(727272 : 121212) + (121212:60606)/(909090:60606)`
`A= 70.(3/14 +1/6 + 2/15)`
`A=70. ((3.15.6)/(14.6.15) + (1.14.15)/(14.6.15) + (2.6.14)/(14.6.15) `
`A=70.(270/1260 + 210/1260 + 168/1260)`
`A=70. (270+210+168)/1260`
`A=70. 648/1260`
`A=70. 38/35`
`A=(70.38)/35`
`A=2660/35`
`A=36`
Vậy `A=36`
