Question

What is 1/3 of 21,
2/5 of 40
4/7 of 280

Answer 1

`A\ fraction\ of\ the\ number\ is\ equal\\to\ the\ product\ of\ the\ fraction\ by\ the\ number.\\\\Therefore:\\\\(1)/(3)\ of\ 21=(1)/(\\ot3_1)\cdot\\ot21^7=1\cdot7=\boxed7\\\\(2)/(5)\ of\ 40=(2)/(\\ot5_1)\cdot\\ot40^8=2\cdot8=\boxed{16}\\\\(4)/(7)\ of\ 280=(4)/(\\ot7_1)\cdot\\ot280^(40)=4\cdot40=\boxed{160}`

Answer 2

`(1)/(3) * 21=(21)/(3)=(7 * 3)/(3)=7 \\ \\ (2)/(5) * 40=(2 * 40)/(5)=(2 * 8 * 5)/(5)=2 * 8=16 \\ \\ (4)/(7) * 280=(4 * 280)/(7)=(4 * 40 * 7)/(7)=4 * 40=160`