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Singapore Math Problem - Help!


tiffany k
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Maybe my brain is just fuzzy today, but I can't see how my son should set this problem up. Thanks for your help!

 

1 mango and 1 papaya together cost $4.70. Krystle bought 2 mangoes and 5 papayas for $13.00. How much did the two mangoes cost?

 

The answer key gives $7.00 as the answer, but I can't figure out how they deduced that number.

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1 mango and 1 papaya together cost $4.70. Krystle bought 2 mangoes and 5 papayas for $13.00. How much did the two mangoes cost?
Forgive the bar diagrams, as I'm not good at doing them in ascii.

 

Two Mangoes and two papayas are $9.40, so 3 papayas are $3.60, and one papaya is $1.20.

 

|---M---|-----P-----|

is $4.70

 

2 mangos and 2 papayas:

|---M---|-----P-----|---M---|-----P-----|

is $9.40

 

2 mangos and 5 papayas:

|---M---|-----P-----|---M---|-----P-----|-----P-----|-----P-----|-----P-----|

is $13.00

 

|-----P-----|-----P-----|-----P-----|

is $13.00-$9.40 = $3.60

and P = $1.20

 

From there, substitute back into one of the original formulas:

 

$4.70-$1.20 = $3.50

One mango is $3.50

 

Two mangos are $7

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1 mango and 1 papaya together cost $4.70. Krystle bought 2 mangoes and 5 papayas for $13.00. How much did the two mangoes cost?
[-------$4.70------][------$4.70------]

[mango+papaya][mango+papaya][papaya][papaya][papaya]

[----------------------------------$13.00--------------------------------]

 

One mango and one papaya makes one unit, and costs $4.70. So Krystle bought 2 units plus three more papayas for $13.00. 2 units cost $9.40, so the three papayas cost $3.60, and each papaya cost $1.20. She bought 5 papayas total, so at $1.20 apiece, it was $6.00 for them. That leaves $7.00 out of the total $13.00, so the 2 mangos must have cost $7.00.

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