Video Transcript
I have two-quarters, two dimes, and one penny. Which coins can I add to make one dollar?
We’re trying to make a total of one dollar. In order to do that, we’ll need to know how much money I already have. Two-quarters, two dimes, and one penny add up to how much money? How much money is two-quarters equal to? We would multiply the two-quarters I have by the value of one-quarter. Two times 25 cents equals 50 cents. 25 plus 25 equals 50.
We can follow the same procedure for our two dimes: two multiplied by 10 cents. Two times 10 equals 20. Two times 10 cents equals 20 cents. One penny is equal to one cent. And we write that 0.01. And then, we add all these three values together: 50 cents plus 20 cents plus one cent. All the way on the right, we have zero, zero, one. Zero plus zero plus one equals one. Moving to the left, five plus two equals seven. Bring down the decimal point, bring down the zero, and bring down the dollar sign. We have 71 cents and we need one dollar.
To find out how much money we need, we subtract 71 cents from one dollar. Starting all the way on the right, we can’t subtract one from zero. So we borrow and then we have one taken out of 10. 10 minus one equals nine and nine minus seven equals two. Bring down the decimal place. Zero minus zero equals zero and copy down our dollar sign. We are missing 29 cents.
Which of the answer choices on the left is equal to 29 cents? Answer choice a has two dimes that equals 20 cents and four nickels. Nickels are worth five cents and we have four of them. Four times five is 20. This means that answer choice a is too much.
We’ve already discovered that four nickels equals 20 cents, four pennies equals four cents, 20 cents plus four cents equals 24 cents. Answer choice b is not enough.
Moving on to answer choice c, one-quarter equals 25 cents, four pennies equals four cents, 25 cents plus four cents equals 29 cents — the exact amount we were looking for. By adding one-quarter and four pennies to the money I already have, I will have exactly one dollar.
Answer choice d and e are both too much, leaving us with a final answer of one-quarter and four pennies.
