Question

Out of $900$ batteries, $517$ batteries are not working properly. If $258$ good batteries are additionally bought, how many batteries are available for use?

• A. $614$
• B. $461$
• C. $641$
• D. $383$

Answer 1

The correct option is C $641$

To find the number of batteries working properly, we subtract $517$ from $900$.
We use the partial sum strategy to subtract $517$ from $900$.

• $900$ can be written as $800+90+10$.
• $517$ can be written as $500+10+7$.
• We subtract $7$ from $10$ to get $3,10$ from $90$ to get $80$, and $500$ from $800$ to get $300$.
• Hence, $900-517=383$.

To find the total number of batteries available for use, we add $383$ and $258$.
We use the partial sum strategy to add $383$ and $258$.

• $383$ can be written as $300+80+3$.
• $258$ can be written as $200+50+8$.
• We add $3$ and $8$ to get $11,80$ and $50$ to get $130$, and $300$ and $200$ to get $500$.
• Hence, $383+258=641$.
• There are a total of $641$ batteries available for use.

Hence, option D is the correct answer.