Gujarat BoardEnglish MediumSTD 9MathsNumber systems1 Mark
MCQ
If 102y= 25, then 10-y equals:
A
$-\frac{1}{5}$
B
$\frac{1}{50}$
C
$\frac{1}{625}$
D
$\frac{1}{5}$
✓
Answer
$\frac{1}{5}$ Solution: We have to find the value of 10-y Given that 102y= 25, therefore, 102y= 25 (10y)2 = 52 $(10^\text{y})^{2\times\frac{1}{2}}=5^{2\times\frac{1}{2}}$ $\frac{10^{\text{y}}}{1}=\frac{5}{1}$ $\frac{1}{5}=\frac{1}{10^\text{y}}$ $\frac{1}{5}=10^\text{y}$ Hence the correct option is d.
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