Keddy likes playing math games with his father. His father wrote a mystery number and said, I will get 1.3 when I divide the mystery number by 5.How many tenths are there in this mystery number?
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There are 65 tenths in the mistery number.
Explanation
Let [tex]x[/tex] be the mistery number, which satisfies:
[tex]\begin{aligned}x\div 5&=1.3\\\Rightarrow x&=1.3\times5\\\therefore\ x&=6.5\end{aligned}[/tex]
The question is “how many tenths are there in [tex]x[/tex]?”. Thus, [tex]x[/tex] also satisfies:
[tex]\begin{aligned}x&=k\times\frac{1}{10}\\\end{aligned}[/tex]
Solving it:
[tex]\begin{aligned}\Rightarrow6.5&=k\times\frac{1}{10}\\\Rightarrow\ \ k&=10\times6.5\\\therefore\ k&=\boxed{\ \bf65\ }\end{aligned}[/tex]
CONCLUSION
∴ There are 65 tenths in the mistery number.
[tex] \frac{x}{5} = 1.3 \\ \\ x = 1.3 \times 5 \\ x = 6.5 = \frac{65}{10} = 65 \: tenths[/tex]
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