You can tell without doing any math (just by looking at the answer choices) that the digits involved will be 4, 0, 9. So, how do you tell what the order of magnitude is?
You recognize that the percentage is not quite 10%. You know that 10% of 47 will be 4.7. (The decimal point gets moved one place to the left.) The choice that is not quite 4.7 is answer (b), 4.09.
_____
10% = 10/100 = 0.10 This is 1.0 with the decimal point moved one place left: .10
0.087*47 = 4.089
You recognize that the percentage is not quite 10%. You know that 10% of 47 will be 4.7. (The decimal point gets moved one place to the left.) The choice that is not quite 4.7 is answer (b), 4.09.
_____
10% = 10/100 = 0.10 This is 1.0 with the decimal point moved one place left: .10
0.087*47 = 4.089
