Dạng 3: Tìm X có đáp án

$a)6,4.X=6,4$

$X=\frac{6,4}{6,4}=1$

$b)7,8.X=6,2.7,8$

$X=\frac{6,2.7,8}{7,8}=6,2$

$c)0,65.X=0,65.0,1$

$X=\frac{0,65.0,1}{0,65}=0,1$

$d)8,4.X+1,6.X=10$

$\left(8,4+1,6\right).X=10$

$10.X=10$

$X=\frac{10}{10}=1$

$a)X+3,12=14,6-8,5$

$X+3,12=6,1$

$X=2,98$

$b)X-5,14=\left(15,7+2,3\right).2$

$X-5,14=18.2$

$X=41,14$

$c)31,5-X=\left(18,6-12,3\right):3$

$31,5-X=6,3:3$

$31,5-X=2,1$

$X=29,4$

$d)X.12,5=\left(32,6-10,4\right).5$

$X.12,5=22,2.5$

$X.12,5=111$

$X=8,88$

$e)X:2,2=\left(28,7-13,5\right).2$

$X:2,2=15,2.2$

$X:2,2=30,4$

$X=66,88$

$f)216,4:X=\left(5,24+4,76\right):2$

$216,4:X=10:2$

$216,4:X=5$

$X=43,28$

Lời giải

Ta có $11,209+x<16,0459$

$x<16,0459-11,209$

$x<4,8369$

$Mà x là số tự nhiên lớn nhất nên$x=4

$1)7,2:2,4.X=4,5$

$3.X=4,5$

x=1,5 

$2)9,15.X+2,85.X=48$

$(9,15+2,85).X=48$

$12.X=48$

$X=48:12=4$

$3)\left(15.28-X\right):0,4=200:0,4$

$420-X=200$

$X=420-200=220$

$4)\left(X.0,25+2020\right).2021=\left(50+2020\right).2021$

$X.0,25+2020=50+2020$

$X.0,25=50$

$X=50:0,25=200$

$5)4,25.\left(X+41,53\right)-125=53,5$

$4,25.\left(X+41,53\right)=53,5+125$

$4,25.\left(X+41,53\right)=178,5$

$X+41,53=178,5:4,25$

$X+41,53=42$

$X=42-41,53$

$X=0,47$

$6)53,2:\left(X-3,5\right)+45,8=99$

$53,2:\left(X-3,5\right)=99-45,8$

$53,2:\left(X-3,5\right)=53,2$

$X-3,5=53,2:53,2$

$X-3,5=1$

$x=1+3,5=4,5$