The number of red blood cells per cubic millimetre of blood is approximately 5.5 million. If the average body contains 5 litres of blood, what is the total number of red cells in the body? Write the standard form. (1 litre = 1,00,000 mm3)
The number of red blood cells in blood = 5.5 million = 5500000 mm3
Blood in a body = 5 litres = 500000 mm3 (∵1 litre = 1,00,000 mm3)
∴ The total number of red cells in the body = 5500000 × 500000
= 55 × 5 × 105 × 105
Using the law of exponent, 
= 275 × 1010
= 2.75 × 102 × 1010
= 2.75 × 1012
∴ The standard form is 2.75 × 1012
114