Here is how you should approach this question:

• You have a straight line of 10cm.
• You want to fit two half-circles on that line.
• That means each half circle will take up 5 cm (because 10 ÷ 2 = 5).
• We know that the radius of a circle is half of its diameter. So radius = diameter/2
• Therefore, each half circle will have a radius of 2.5 cm.