Did you ever wonder?

Estu asks: could everyone in Mumbai fit into 1 lakh buses? Make a sensible guess: a bus holds 50 people. Then 1 lakh buses hold 1,00,000 × 50 = 50 lakh people. Mumbai has over 1 crore 24 lakh people (from the table). So no. What about 5000 ships like the Titanic, each carrying about 2500 people?

Roxie asks: travelling 100 km a day, could she reach the Moon in 10 years? The Moon is 3,84,400 km away. Work in stages: a year is 100 × 365 = 36,500 km; ten years is 36,500 × 10 = 3,65,000 km. That is a little short of the Moon. Breaking a big calculation into steps makes it easy.

Calculations can uncover amazing facts:

• 1250 × 380 = 4,75,000: the kīrtanas said to be composed by Purandaradāsa, the 15th-century singer who set out ways of teaching Carnatic music still used today.
• 2100 × 70,000 = 14,70,00,000 km: roughly the Earth–Sun distance (it changes through the year, up to about 152 million km).
• 6400 × 62,500 = 40,00,00,000 litres: the water the Amazon pours into the Atlantic every second. There is fresh water 160 km out to sea!

Division too:

• 13,95,000 ÷ 150 = 9300 km: the longest single train journey in the world, Moscow to Vladivostok, about 7 days. India's longest, Dibrugarh to Kanyakumari, is 4219 km in about 76 hours.
• 10,50,00,000 ÷ 700 = 1,50,000 kg: an adult blue whale can weigh more than this.

Your turn. If 250 babies are born every minute in the world, are a million born in a day? Could you count a million coins in a day at one coin a second? (A day has 24 × 60 × 60 = 86,400 seconds.)