QUESTION

# Prime factors of 140 are:(a) $2\times 2\times 7$(b) $2\times 2\times 5$(c) $2\times 2\times 5\times 7$(d) $2\times 2\times 5\times 7\times 3$

Hint: We will use the definition of prime number and prime factors to find the prime factors of 140. Prime numbers are numbers having only two factors 1 and itself whereas prime factors are factors which are prime.

\begin{align} & 140=1\times 140 \\ & 140=2\times 70 \\ & 140=4\times 35 \\ & 140=5\times 28 \\ & 140=7\times 20 \\ & 140=10\times 14 \\ \end{align}
So factors of the number 140 are 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70. Now among these factors the prime factors according to the definition are 2, 2, 5 and 7 because $140=2\times 2\times 5\times 7$.