Originally the dimensions of a rectangle were 20cm by 23cm. When both dimensions were decreased by the same amount, the area of the rectangle decreases by 120. Find the dimensions of the rectangle.

The answer is 17cm by 20cm.
The original area is 460cm (20x23), minus 120cm gives a new area of 340cm.
20cm-3cm=17cm and 23cm-3cm=20cm
17cmx20cm = 340cm

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post