tính nhanh:
A; 48 + 46 + 50 + 44 + 47 + 43 + 41 + 45
B; 43/20 + 17/6 : {5/8 + 7/30}
C;1/7 : 5/17 + 1/7 : 5/18
giúp mik với, mik cảm ơn mn nhé^^
tính nhanh:
A; 48 + 46 + 50 + 44 + 47 + 43 + 41 + 45
B; 43/20 + 17/6 : {5/8 + 7/30}
C;1/7 : 5/17 + 1/7 : 5/18
giúp mik với, mik cảm ơn mn nhé^^
$A=48 + 46 + 50 + 44 + 47 + 43 + 41 + 45\\A=(46+44)+(47+43)+(48+41)+(50+45)\\A=90+90+89+95\\A=180+89+95\\A=269+95\\A=364\\B= \dfrac{43}{20} + \dfrac{17}{6} : \left \{ \dfrac{5}{8}+\dfrac{7}{30} \right \}\\B=\dfrac{43}{20}+\dfrac{17}{6}:\dfrac{103}{120}\\B=\dfrac{43}{20}+\dfrac{17}{6}.\dfrac{120}{103}\\B=\dfrac{43}{20}+17.\dfrac{20}{103}\\B=\dfrac{43}{20}+\dfrac{340}{103}\\B=\dfrac{11229}{2060}\\C=\dfrac{1}{7} : \dfrac{5}{17} + \dfrac{1}{7} : \dfrac{5}{18} \\C=\dfrac{1}{7}.\dfrac{17}{5}+\dfrac{1}{7}.\dfrac{18}{5}\\C=\dfrac{1}{7}\left ( \dfrac{17}{5}+\dfrac{18}{5} \right )\\C=\dfrac{1}{7}.7=1$
Đáp án:
A = 48 + 46 + 50 + 44 + 47 + 43 + 41 + 45
= ( 46 + 43 ) + ( 48 + 41) + ( 50 + 45) + ( 47 + 43)
= 89 + 89 + 95 + 90 = 363
B = 43/20 + 17/6 : {5/8 + 7/30}
= 43/20 + 17/6 : 103/120
= 43/20 + 340/103 = 11229/2060
C = 1/7 : 5/17 + 1/7 : 5/18
= 1/7 . 17/5 + 1/7 . 18/5
= 1/7(17/5 + 18/5) = 1/7 . 7 = 1
Giải thích các bước giải: