Adding big numbers

In your book, Maths Mela (Chapter 4, We the Travellers — II), a lorry has 28 litres of fuel in its tank, and 75 litres more are filled. How much fuel is in it now? We add 28 l + 75 l. Ones first: 8 + 5 = 13 ones. That is 1 ten and 3 ones, so we write 3 and carry 1 ten. Tens: 2 + 7 + 1 = 10 tens, which is 1 hundred and 0 tens. So the lorry has 103 l of fuel.

Some sums have an easier way. 99 is just 1 less than 100, so 46 + 99 = 46 + 100 − 1 = 145. In the same way, 5 + 89 = 5 + 90 − 1 = 94.

Big numbers are added in exactly the same way: keep ones under ones, tens under tens, hundreds under hundreds, and so on, and carry whenever a place reaches 10 or more. In 2019, the North–South Corridor from Srinagar to Kanniyakumari was the longest land route in India. A place on it was 1,855 km from Srinagar and 1,862 km from Kanniyakumari. Ones: 5 + 2 = 7. Tens: 5 + 6 = 11 tens, so write 1 and carry 1 hundred. Hundreds: 8 + 8 + 1 = 17, write 7 and carry 1 thousand. Thousands: 1 + 1 + 1 = 3. The corridor was 3,717 km long.

5-digit numbers work the same way. Mahesh and his family drive from Srinagar to Kanniyakumari. He spends ₹21,880 on fuel and toll tax and ₹38,900 on other things. ₹21,880 + ₹38,900 = ₹60,780. If the digits are kept in line, we do not even need to write TTh, Th, H, T and O at the top.