Bài 1:
a) 79.283 + 21.301 + 79.17 - 21 = 79.(283 + 17) + 21.(301 - 1)
= 79.300 + 21.300
= 23700 + 6300
= 30000
b) $\text{$8^{19}$ : $8^{18}$ . 8 + 4 . $3^{2}$ - $1^{2018}$}$ = 8 . 8 + 4 . 9 - 1
= 64 + 36 - 1
= 100 - 1
= 99
c) 700 + {5 .[60 : (5 - 3 . $7^{0}$)] - $10^{2}$} = 700 + {5 .[60 : (5 - 3 . 1)] - 100}
= 700 + {5 .[60 : (5 - 3 )] - 100}
= 700 + {5 .[60 : 2] - 100}
= 700 + {5 .30 - 100}
= 700 + {150 - 100}
= 700 + 50
= 750
Bài 2:
a) 4x - 69 : 23 = 37
4x - 3 = 37
4x = 37 + 3
4x = 40
x = 40 : 4
x = 10
b) 123 - 5.(2x + 3) = 3.$4^{2}$
123 - 5.(2x + 3) = 3.16
123 - 5.(2x + 3) = 48
5.(2x+3) = 123 - 48
5.(2x+3) = 75
2x + 3 = 75 : 5
2x + 3 = 15
2x = 15 - 3
2x = 12
x = 12 : 2
x = 6
c) Vì 24 $\vdots$ x , 60 $\vdots$ x , 150 $\vdots$ x nên x ∈ ƯC (24,60,150) (5 < x < 20 ; x ∈ N)
Ta tìm ƯC thông qua ƯCLN :
Ta có : 24 = $2^{3}$ . 3
60 = $2^{2}$ . 3 . 5
150 = 2 . 3 . $5^{2}$
ƯCLN (24, 60, 150) = 2 . 3 = 6
ƯC (24, 60, 150) = Ư (6) = {1 ; 2 ; 3 ; 6}
Mà 5 < x < 20 nên x = 6
