I have invented a trick to get the number thought by your child.If you want to know my math trick then following steps are given below

step 1.ask your child to think a number but not tell the thought number.

step 2.ask your child to multiply it by 2.

step 3.ask your child to substract it by his or her thought number.

step 4.ask your child to annunce the final answer of all calculations done by your child in his or her mind.