A money box contains only 10-cent and 20-cent coins. There are 40 coins with a total value of $6.50. How many coins of each?

10x+20y= 350

Step-by-step explanation:

Add the decimal. 3.50

Let's assume that all the coins are 10-cent coins.

The total value would be 10 x 40 = 400 cents = $4

So, it would be $2.5 less than the actual total value,

We now know that not all the coins are 10-cent coins, so now we will replace 1 10-cent coins with a 20-cent coins.

Everytime we switch a 1 10-cent coins to a 20-cent coins, the value go up 10 cents. So, we need to switch 25 times (to make the value goes up $2.5)

-> There are 25 20-cent coins and 15 10-cent coins

Recheck : 25 x 20 + 15 x 10 = 500 + 15 = 650 cents = $6.5

the answer is the third / last answer

step-by-step explanation: