Đáp án:
Giải thích các bước giải:
a) `78xx31+78xx24+78xx17+22xx72`
`=(72+6)xx31+(72+6)xx24+(72+6)xx17+22xx72`
`=72xx31+6xx31+72xx24+6xx24+72xx17+6xx17+22xx72`
`=72xx(31+24+17+22)+6xx(31+24+17)`
`=72xx(31+24+17+22)+6xx72`
`=72xx(31+24+17+22+6)`
`=72xx100`
`=7200`
b) $5,28:0,25+4,72\times 4-37$
`=5,28xx4+4,72xx4-37`
`=4xx(5,28+4,72)-37`
`=4xx10-37`
`=40-37`
`=3`
c) `1/6xx(1 1/2-3/4)+0,25`
`=1/6xx(3/2-3/4)+1/4`
`=1/6xx3/4+1/4`
`=3/24+1/4`
`=3/8`
d) `3+6+9+...+99` (Có $(99-3):3+1=33$ số hạng)
`=(3+99)+(6+96)+(9+93)+...` (Có $33:2=16,5$ cặp)
`=102+102+102+...`
`=102xx16,5`
`=1683`
