Question 1135445
Let {{{ n }}} = the number of weeks that have gone by
Let {{{ A }}} = the amount saved up to week number {{{ n }}}
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The amount she has paid up to week {{{ n }}} is:
{{{ n = 1 }}}
{{{ 75 + 50n  = 75 + 50*1 }}}
{{{ A = 125 }}}
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{{{ n = 2 }}}
{{{ 75 + 50n = 75 + 50*2 }}}
{{{ A = 175 }}}
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{{{ n = 3 }}}
{{{ 75 + 50n = 75 + 50*3 }}}
{{{ A = 225 }}}
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you can continue this table
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The equation is:
{{{ A = 75 + 50n }}}
When does the amount, {{{ A = 600 }}} ?
{{{ 600 = 75 + 50n }}}
{{{ 50n = 600 - 75 }}}
{{{ 50n = 525 }}}
{{{ n = 10.5 }}}
{{{ 10 }}} weeks won't be quite enough time, so
the answer is {{{ 11 }}} weeks