S K Gupta and Anubhuti Gangal Solutions for Exercise 7: Mental Maths

What is the L.C.M of $9$ and $18?$

Find the L.C.M of $5$ and $7$.

What is the H.C.F of $5, 10$ and $15$?

What is the H.C.F of $8, 12$ and $20$?

Find the least multiple of $5$ which is divisible by both $2$ and $3?$

Which of the following are the prime numbers?

Write down the numbers between $10$ and $20$ which have exactly $2$ factors.

Find the sum of all the prime numbers between $1$ and $10$.