Find the HCF of $0.7,0.35,1.05$.

Let's convert the decimal numbers to fractions:
$$0.7=\frac{70}{100}$$

$$0.35=\frac{35}{100}$$

$$1.05=\frac{105}{100}$$

Formula for HCF of fractions:

$$\text{HCF}=\frac{\text{HCF of Numerators}}{\text{LCM of Denominators}}$$

Numerators are $70,35,105$:

$$\text{HCF}(70,35,105)=35$$

Denominators are $100,100,100$:

$$\text{LCM}(100,100,100)=100$$

So, the HCF is:

$$\text{HCF}=\frac{35}{100}=0.35$$