Đáp án:
`a,`
`(4/15 + 7/12 - 19/20) × 2,5 + 0,25`
`= (17/20 - 19/20) × 2,5 + 1/4`
`= (-1)/10 × 2,5 + 1/4`
`= (-1)/4 + 1/4`
`= 0`
`b,`
`30 + 2,8 ÷ (4/25 - 9/15 - 1/6)`
`= 30 + 14/5 ÷ ((-11)/25 - 1/6)`
`= 30 + 14/5 ÷ (-91)/150`
`= 30 + 14/5 × (-150)/91`
`= 30 + (-60)/13`
`= 330/13`
`c,`
`(2 1/3 + 3 1/2) ÷ (-4 1/6 + 3 1/7) + 7,5`
`= (7/3 + 7/2) ÷ ( (-25)/6 + 22/7) +15/2`
`= 35/6 ÷ (-43)/42 + 15/2`
`= 35/6 × (-42)/43 + 15/2`
`= (-245)/43 + 15/2`
`= 155/86`
