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Question

Sara and David had $420 altogether. Sara spent 2/5 of her money and David spent $120. After spending, Sara had twice as much money as David. How much money did David have at first?

Answer

I think something is wrong with the numbers. My solution is below but the money is in fractions of 13.

THOUGHT PROCESS
When we see 2/5, we might have the impulse to draw 5 units with
2 spent and 3 remaining. However the 3 remaining is twice as much
as David's, which means we have to cut the units in halves.
So it is better to do 10 units instead of 5.

MODEL
WORKING
   10 u + 3u + 120 = 420
   u = 300/13

At first, David had 3u + 120 = 900/13 + 120 = $189 3/13.

CHECK:
         Sara        David
Before:  230 10/13   189 3/13    (TOTAL: 420)
After:   1800/13     900/13      (Sara = 2 x David)




 

1 Reply 2 Likes

Thanks! I was getting decimals too!

0 Replies 0 Likes