1.

Explain why 7 × 11 × 13 + 13 and 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 are composite numbers.

Answer»

(i) 7 × 11 × 13 + 13 = 13 × [7 × 11 + 1] 

= 13 × 78 

This is composite number. 

(ii) 7 × 6 × 5 × 4 × 3 × 2 × 1 + 5 

= 5 × {7 × 6 × 5 × 4 × 3 × 2 + 1} 

= 5 × 1009. 

This is composite number.



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