Math problem general

Question

In one week, the pumpkin vines grow 3 cms. Today the vines are 20cms long. How long were the vines two weeks ago?

Answer 1

It can help to visualize a problem like this. Since we're talking about the length of a vine, a good visual would be a number line.

Start with a number line ending at 20 cm, which is the current length of the vine. Then jump back on the number line 3 cm segments for each prior week. Since we jump back two 3cm segments, we land on 14.

This is visualizing the action of subtracting those segments on the number line.

Answer 2

If the vine measures 20cm now, in order to calculate the length two weeks ago, we need to SUBTRACT two weeks' worth of growth. The vine grows at 3cm per week, so for two weeks, it would be:

3cm x 2wks = 6cm

Then subtract this quantity from the current measurement:

20cm - 6cm = 14cm

The vines measured 14cm two weeks ago.