Adam wants to buy a video game system that costs $100.00. he has $28.35 in one piggy bank and $31.90 in another piggy bank. how much more money does adam need before he can buy the video game system?

how can estimation be used to make sure the answer is reasonable?

a.
adam needs $160.25 more.
estimation: $28 + $32 = $60.
$100 + $60 = $160.
adam needs about $160 more to buy his video game system.

b.
adam needs $39.75 more.
estimation: $28 + $32 = $60.
$100 – $60 = $40.
adam needs about $40 more to buy his video game system.

c.
adam needs $30.13 more.
estimation: $28 + $32 = $60.
$60 ÷ 2 = $30.
adam needs about $30 more to buy his video game system.