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Stumped by 10 year old's maths homework question. Help!

  • 05-02-2020 8:15pm
    #1
    dark crystal
    Registered Users, Registered Users 2 Posts: 10,962 ✭✭✭✭


    The product of two numbers is 40. The difference between them is 3. What are the two numbers?

    I cannot for the life of me work it out...can anyone help??


Comments

  • #2
    is_that_so
    Registered Users, Registered Users 2 Posts: 32,136 ✭✭✭✭is_that_so


    I means multiplied by - for example 4X3 and 12 is the product.


  • #3
    un5byh7sqpd2x0
    Closed Accounts Posts: 1,862 ✭✭✭un5byh7sqpd2x0


    5 and 8


  • #4
    I Am The Law
    Registered Users, Registered Users 2 Posts: 657 ✭✭✭I Am The Law


    5 x 8


  • #5
    ectoraige
    Registered Users, Registered Users 2 Posts: 2,105 ✭✭✭ectoraige


    dark crystal wrote: »
    The product of two numbers is 40. The difference between them is 3. What are the two numbers?

    I cannot for the life of me work it out...can anyone help??

    Product means multiplication, so what two numbers multiplied together make 40?

    There's 1x40, 2x20, 4x10, and 5x8.

    Difference means substraction so which pair had a difference of 3?

    5 and 8 is the answer


  • #6
    is_that_so
    Registered Users, Registered Users 2 Posts: 32,136 ✭✭✭✭is_that_so


    Seriously people, doing the child's homework by giving up the answer?! I dunno.:)


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  • #7
    dark crystal
    Registered Users, Registered Users 2 Posts: 10,962 ✭✭✭✭dark crystal


    Thank you so much everyone! I was trying to work out every combination of numbers that added up to 40, but multiplication never entered my clearly empty head.

    And I'm usually so good at Countdown...:o


  • #8
    Yakuza
    Registered Users, Registered Users 2 Posts: 5,141 ✭✭✭Yakuza


    -8 and -5 also works :) (not sure it's appropriate for a 10-year old though :))

    To work it out analytically instead of brute force:
    Let x be the lower number, so x+3 will be the higher one.
    x*(x+3) = 40, or x²+3x - 40 = 0.
    Banging this into the good old Quadratic Equation formula (with a=1, b=3 and c = -40) yields -8 and 5 for x (so the other number being -5 or 8).


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