Yu
Lv 6
Yu asked in 科學及數學數學 · 1 decade ago

maths,,,,,,,,,,,,,,,,,help.................

3. Bobby saves a fixed amount of money every day.He finds that the price of a model is $70 more than his savings in 5 days or $10 more than his savings in 9 days.How much does he save each day?

4. Donna buys some $2 stamps and some $5 stamps. If she spends $54 altogether and gets 15 stamps,how many $2 stamps does she buy?

Update:

要有設and答,and 未知數,例如:a,f,b......

1 Answer

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  • 1 decade ago
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    3〉Let Bobby save $n every day&the model's price is $x

    then

    5n=x-70 ---1

    9n=x-10 ---2

    from 1

    5n=x-70

    5n+70=x ---3

    from 2

    9n=x-10

    9n+10=x ---4

    (將3=4)

    5n+70=9n+10

    70-10=9n-5n

    60=4n

    n=60/4

    n=15

    ∴Bobby save $15 each day.

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