Cristiano is saving money to buy a bike that costs $189. He has saved $99 so far. He plans on saving $10 each week. In how many weeks will he have enough money to buy the bike?

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Answer 1 · 2016-12-17T20:25:40

It will take Cristiano 9 weeks to have enough money.

We can write a formula for this problem as:

$$189 = $99 + $10w$

$189 is the total amount Cristiano need.

$99 is what Cristiano already has.

$10w is the $10 per week Cristiano plans on saving for $w$ weeks until he has saved the full $189.

Solving for $w$ gives:

$$189 - $99 = $99 - $99 + $10w$

$$90 = 0 + $10w$

$$90 = $10w$

$($90)/($10) = ($10w)/($10)$

$(cancel($)90)/(cancel($)10) = (cancel($10)w)/(cancel($10))$

$90/10 = w$

$9 = w$