\( \begin{array}{l}\text { HCF }=150 \\ \text { Express } 6 \mathrm{~km} \text { m } 4000 \mathrm{~m} \text { in the simplest form. } \\ 6000 \mathrm{~m}: 4000 \mathrm{~m} \\ 6000 \quad \frac{4000}{2000}\end{array} \)

To express 6 km 4000 m in the simplest form, first convert everything to meters. Since 6 km equals 6000 m, you get a total length of \( 6000 + 4000 = 10000 \) m. Now, you can represent this as a ratio: \[ \frac{10000}{4000}. \] To simplify this fraction, divide both the numerator and denominator by their HCF, which is 2000: \[ \frac{10000 \div 2000}{4000 \div 2000} = \frac{5}{2}. \] Thus, \( 6 \text{ km } 4000 \text{ m} \) simplifies to \( 5:2 \). To ensure you're simplifying ratios correctly, always check for any common factors before dividing. One common mistake is to overlook the need for reducing fractions further when they're presented as a ratio. Always look for the highest common factor to streamline your calculation!