This question was previously asked in

HTET PRT 2014 - 2015 Official Paper

Option 3 : 40a^{7}

**Given**

2^{3} × a^{3} × 5a^{4}

**Concept**

By using exponents method, when two numbers or variable in multiplication form and having the same base then the power of that number or variable is added.

Formula ; ma × mb = m( a + b )

**Calculation**

2^{3} = 2× 2 × 2 =8

a^{3} × 5a^{4} [ Here base of a^{3} and 5a^{4} is same which is 'a' ]

∴ a^{3} × 5a^{4} = 5a^{( 3 + 4 )} = 5a^{7}

now

⇒ 2^{3} × a^{3} × 5a^{4} = 8 × 5a^{7} = 8 × 5 × a^{7} = 40a^{7}

**∴ 2 ^{3} × a^{3} × 5a^{4} = 40a^{7} **