+414 Tom had a total of 120 red and blue marbles. 30% of them were red marbles. His father gave him some more red marbles, after which the percentage of red marbles increased to 40%. How many red marbles did Tom's father give him?
+33614 30% of 120 is 36, so Tom originally had 36 red marbles. If his father gave him n red marbles then
36+n = (120 + n)*40/100 Multiply through by 10 and simplify:
360 + 10n = 480 + 4n Subtract 4n from both sides
360 + 6n = 480 Subtract 360 from both sides
6n = 120 Divide both sides by 6
n = 20
Tom's father gave him 20 red marbles.
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+33614 30% of 120 is 36, so Tom originally had 36 red marbles. If his father gave him n red marbles then
36+n = (120 + n)*40/100 Multiply through by 10 and simplify:
360 + 10n = 480 + 4n Subtract 4n from both sides
360 + 6n = 480 Subtract 360 from both sides
6n = 120 Divide both sides by 6
n = 20
Tom's father gave him 20 red marbles.
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