How much money did I have before buying 15 burgers?

[leprofece]

After I have purchased 15 same-priced burgers it remains 380 dollars and 470 fails me to buy another how much DiD I have? Answer $ 13130
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Answer 13130 dollars
Despite I think it is a bad answer

 

[Opalg]

After I have purchased 15 same-priced burgers it remains 3.80 dollars and 4.70 fails me to buy another how much DiD I have? Answer $ 131.30

I think that those amounts of money are unrealistically large. I have inserted a decimal point to bring them down to size.

If you have $\$3.80$ remaining, and you need an extra $\$4.70$ to buy an additional burger, then the price of a burger must be $\$3.80 + \$4.70 = \$8.50$. The cost of 15 burgers would then be $\$8.50 \times 15 = \$127.50$. Having spent that amount, you have $\$3.80$ remaining. Therefore you must have started with $\$127.50 + \$3.80 = \$131.30$.