Random Puzzles 

Workings

Hint
There are three feet in a yard, and 1,760 yards in a mile.

Answer
Seconds in a week.

Reasoning
There are 60 x 60 x 24 x 7 = 604,800 seconds in a week.

There are 3 x 1760 x 100 = 528,000 feet in 100 miles.

Workings

Hint
helium = h-- + l--

Answers
helium = hum + lie latest = let + sat almond = man + old eldest = led + set placed = cap + led radium = air + mud desert = red + set wealth = law + the tricky = cry + kit funnel = elf + nun
Alternative Answers
The following answers use less common words.

helium = him + leu
helium = hue + mil
helium = hum + lei

latest = els + tat

almond = don + lam
almond = lam + nod

eldest = eld + set
eldest = els + ted

placed = pec + lad

radium = mud + ria
radium = amu + rid
radium = aid + rum

wealth = awl + the
wealth = haw + let

There are more answers with even rarer words, but I've chosen not to include those.

Workings

Hints
Five of the missing first letters are: F, P, T, C, B.

Answers
--pay = repay --lad = salad --ior = prior --eue = queue --rva = larva --day = today --voc = havoc --yss = abyss --gun = begun --pty = empty --til = until --cay = decay --uke = fluke --uze = gauze --noe = canoe

Workings

Hint
Think about the number of legs.

Answer
There are 7 chickens, 28 mice and 280 ants.

Reasoning
For every chicken (2 legs) we have 4 mice (16 legs) and 40 ants (240 legs) = 258 legs.

So we can divide the total number of legs by 258, giving 1,806 ÷ 258 = 7 (chickens).