Adding and subtracting dollars and cents

In the last lesson, you subtracted money by renaming. Here are ten ten-cent coins. Ten ten-cents make one dollar. Today we add and subtract money by lining up the decimal points. Kavin buys a storybook for twelve dollars and sixty-five cents and a water bottle for four dollars and eighty-five cents. How much does he pay altogether? We must find the total price. So we add the two prices. Write the storybook price on top. Write the bottle price below. Line up the decimal points. Tens and dollars go on the left of the point. Ten-cents and cents go on the right. Start with the cents. Five plus five is ten. Rename ten cents as one ten-cent and zero cents. Write the one ten-cent on top of the ten-cents. Now the ten-cents. Six plus eight is fourteen. Add the 1 on top. Fourteen plus one is fifteen. Ten ten-cents make one dollar. Rename fifteen ten-cents as one dollar and five ten-cents. Write the one dollar on top of the dollars. It crosses the decimal point. Write the decimal point in the answer. It lines up with the other decimal points. Now the dollars. Two plus four is six. Add the 1 on top. Six plus one is seven. In the tens, there is nothing to add to the 1. Write the 1. Kavin pays seventeen dollars and fifty cents altogether. When we subtract, we rename the other way, one dollar into ten ten-cents.

Lin has five dollars and seventy cents. Her grandmother gives her three dollars and forty-five cents. How much money does Lin have now? Try it first. Pause if you like. Start with the cents. Zero plus five is five. Now the ten-cents. Seven plus four is eleven. Ten ten-cents make one dollar. Rename eleven ten-cents as one dollar and one ten-cent. Write the one dollar on top of the dollars. It crosses the decimal point. Now the dollars. Five plus three is eight. Add the 1 on top. Eight plus one is nine. Lin has nine dollars and fifteen cents now.

Kavin has fifteen dollars and thirty cents. He spends three dollars and eighty cents on a snack. How much money does he have left? Try it first. Pause if you like. Start with the cents. Zero minus zero is zero. Now the ten-cents. We cannot subtract eight ten-cents from three ten-cents. Rename one dollar as ten ten-cents. Five minus one is four. The one dollar moves over the decimal point. It is now ten ten-cents. Ten ten-cents and three ten-cents make thirteen ten-cents. Thirteen minus eight is five. Four minus three is one. In the tens, there is nothing to subtract from the 1. Write the 1. Kavin has eleven dollars and fifty cents left. Line up the decimal points, and remember that ten ten-cents make one dollar.