Pablo made 4 stacks of toy blocks. The first stack was 5 blocks tall. The second stack was 2 blocks taller than the first. The third stack was 5 blocks shorter than the second stack, and the last stack was 5 blocks taller than the third stack. How many toy blocks did Pablo use in all? Let's be accurate as possible.
The number of blocks in the second stack is 5 + 2 = 7. The number of blocks in the third stack is 7 − 5 = 2. The number of blocks in the last stack is 2 + 5 = 7. Pablo used 5 + 7 + 2 + 7 = 21 toy blocks in all.
The answer: 21.