Question

HCF of 21,39,and 87 is:​

Answer 1

Answer:

3

Step-by-step explanation:

Decompose all numbers into prime factors ⟱⟱

$\begin{array}{r | l} 3 & 21 \\ \cline{2-2} 7 & 7 \\ \cline{2-2} & 1 \end{array}$  

$\begin{array}{r | l} 3 & 39 \\ \cline{2-2} 13 & 13 \\ \cline{2-2} & 1 \end{array}$

$\begin{array}{r | l} 3 & 87 \\ \cline{2-2} 3 & 27 \\ \cline{2-2} 3 & 9\\ \cline{2-2} 3 & 3 \\ \cline{2-2} & 1 \end{array}$

Write all numbers as the product of its prime factors ⟱⟱

Factor of 21 => 3 × 7

Factors of 39 => 3 ×13

Factors of 87 => 3 × 3 × 3 × 3

So the HCF of 21,39,and 87 and 72 is 3

Answer 2

Answer:

21 = 3 × 7

39 = 3 × 13

87 = 3 × 29

So, highest common factor is 3. Because 3 is common in all.

HCF = 3