Decimals by tens

Find the value of eighty four divided by two hundred without using a calculator. Try it first. Pause if you like. Two hundred is one hundred times two. Divide by one hundred first, then by two. Keep the decimal point fixed. Each column gives a digit its value. Eighty four divided by one hundred is zero point eight four. Move the digits two places to the right to divide by one hundred. Keep the divide by two. Split zero point eight four into zero point eight and zero point zero four. Zero point eight divided by two is zero point four. Zero point zero four divided by two is zero point zero two. Zero point four plus zero point zero two is zero point four two. Zero point eight four divided by two is zero point four two. To divide by ten, move one place right. By one hundred, two places right. By one thousand, three places right. Dividing by ten, one hundred or one thousand gives a smaller number. The decimal point stays fixed.

Find the value of two point zero four five times three hundred without using a calculator. Try it first. Pause if you like. Three hundred is three times one hundred. Multiply by three first, then by one hundred. Multiply each part by three. Two times three is six. Zero point zero four times three is zero point one two. Zero point zero zero five times three is zero point zero one five. Six plus zero point one two plus zero point zero one five is six point one three five. Two point zero four five times three is six point one three five. Keep the times one hundred. Six point one three five times one hundred is six hundred and thirteen point five. Multiplying by one hundred moves the digits two places to the left. The point stays still. To multiply by ten, move one place left. By one hundred, two places left. By one thousand, three places left.

Find the value of three point six times forty without using a calculator. Try it first. Pause if you like. Forty is four times ten. Both factors are needed. Three times four is twelve. Zero point six times four is two point four. Twelve plus two point four is fourteen point four. Three point six times four is fourteen point four. Keep the times ten. Fourteen point four times ten is one hundred and forty four. Multiply by ten. Every digit moves one place to the left of where it was. Each digit has its value from its place. A multiple has two factors, and we use both.