#3**+2 **

This may help, if multiplying by 9 mentally is difficult. A lot of these mental tricks I wish I knew earlier on.

\(15*9\) | Let's make it simpler. |

\(15(10-1)\) | Obviously, this is the same thing. Now, distribute the 15 to both terms. |

\(15*10-15*1\) | Now, simplify. This is much easier, don't you think? |

\(150-15\) | And just in case borrowing is another mental headache... |

\(150-(20-5)\) | Yet again, I have not changed the expression at all. |

\(150-20+5\) | Simplify. |

\(130+5\) | |

\(135\) | |

This may look like a lot of steps, but all we are doing is making the problem easier. With practice, this will simplify multiplication with large numbers.

TheXSquaredFactor Oct 10, 2017