PRESENTATION OUTLINE
UNDERSTAND
There is a total of 100 blocks and 95% of them are red. Some of the red blocks are removed and after this 75% of blocks are red. What is the number of blocks removed from the bag?
PLAN
We used the Strategy guess and check, and work it out:)because we need to be sure of our answer to be correct.
SOLVE
We knew that 5/20 is equal to 25% and 15/20 equals 75%. So if there was 95/100 red blocks and 5/100 other blocks and then if you cut 80 red blocks that brings 5 other blocks to 25% and the 15 red blocks to 75%. So our answer is 80 red blocks are removed from the bag.
CHECK
We redid our work backwards. We added 20 and 80 to get 100 again and so we were absolutely sure that 80 was the answer!
