Đáp án:
a.
`25% × m + 3/4 × m = 30`
`1/4 × m + 3/4 × m = 30`
`(1/4 + 3/4) × m = 30`
`1 × m = 30`
`m = 30 : 1`
`m = 30`
Vậy `m = 30`
b.
`m = 2017 - 2016 + 2015 - 2014 + 2013 - 2012 + 2011 - 2010`
`m = (2017 - 2016) + (2015 - 2014) + (2013 - 2012) + (2011 - 2010)`
`m = 1 + 1 + 1 + 1`
`m = 4`
Vậy `m = 4`