WORK+BACKWARDS


 * Working Backwards **

Question: Jack walked from Santa Clara to Palo Alto. It took 1 hour 25 minutes to walk from Santa Clara to Los Altos. Then it took 25 minutes to walk from Los Altos to Palo Alto. He arrived in Palo Alto at 2:45 P.M. At what time did he leave Santa Clara?

Strategy:

1) UNDERSTAND:

What do you need to find?

You need to find what the time was when Jack left Santa Clara.

2) PLAN:

How can you solve the problem?

You can work backwards from the time Jack reached Palo Alto. Subtract the time it took to walk from Los Altos to Palo Alto. Then subtract the time it took to walk from Santa Clara to Los Altos.

3) SOLVE:

Start at 2:45. This is the time Jack reached Palo Alto. Subtract 25 minutes. This is the time it took to get from Los Altos to Palo Alto. Time is: 2:20 P.M.

Subtract: 1 hour 25 minutes. This is the time it took to get from Santa Clara to Los Altos..

Jack left Santa Clara at 12:55 P.M.

LEARN ABOUT IT

To solve some problems, you may need to undo the key actions in the problem. This strategy is called Work Backward.

The castle kitchen servants brought in 4 pies left over from the feast. 12 pies were eaten at the feast. Queen Mab took 2 home with her. How many pies did the servants bring into the feast at the beginning?


 * First, I'll account for all the pies that were eaten or taken home.
 * 12 + 2 = 14
 * Then I'll add the 4 pies that were left over.
 * 14 + 4 + 18
 * Therefore, there must have been 18 pies at the start of the feast.